Unable to install patch SUPEE-8788 on magento version 1.9.0.1

Question

While trying to install patch SUPEE-8788 I am getting the following error. I have already installed the patch SUPEE-3941

Checking if patch can be applied/reverted successfully...
ERROR: Patch can't be applied/reverted successfully.

patching file app/code/core/Mage/Adminhtml/Block/Catalog/Product/Helper/Form/Gallery/Content.php
patching file app/code/core/Mage/Adminhtml/Block/Cms/Wysiwyg/Images/Content/Uploader.php
patching file app/code/core/Mage/Adminhtml/Block/Dashboard/Graph.php
patching file app/code/core/Mage/Adminhtml/Block/Media/Uploader.php
patching file app/code/core/Mage/Adminhtml/Block/Urlrewrite/Category/Tree.php
patching file app/code/core/Mage/Adminhtml/Model/System/Config/Backend/Serialized.php
patching file app/code/core/Mage/Adminhtml/controllers/DashboardController.php
patching file app/code/core/Mage/Adminhtml/controllers/IndexController.php
Hunk #1 succeeded at 373 (offset -19 lines).
patching file app/code/core/Mage/Adminhtml/controllers/Media/UploaderController.php
patching file app/code/core/Mage/Catalog/Helper/Image.php
patching file app/code/core/Mage/Catalog/Model/Resource/Layer/Filter/Price.php
patching file app/code/core/Mage/Catalog/etc/config.xml
patching file app/code/core/Mage/Catalog/etc/system.xml
patching file app/code/core/Mage/Centinel/Model/Api.php
patching file app/code/core/Mage/Centinel/Model/Api/Client.php
patching file app/code/core/Mage/Core/Block/Abstract.php
patching file app/code/core/Mage/Core/Helper/Url.php
patching file app/code/core/Mage/Core/Model/Encryption.php
patching file app/code/core/Mage/Core/Model/Input/Filter/MaliciousCode.php
patching file app/code/core/Mage/Core/functions.php
patching file app/code/core/Mage/Customer/Block/Address/Book.php
patching file app/code/core/Mage/Customer/controllers/AddressController.php
patching file app/code/core/Mage/Dataflow/Model/Profile.php
patching file app/code/core/Mage/Downloadable/Block/Adminhtml/Catalog/Product/Edit/Tab/Downloadable/Links.php
patching file app/code/core/Mage/Downloadable/Block/Adminhtml/Catalog/Product/Edit/Tab/Downloadable/Samples.php
patching file app/code/core/Mage/Downloadable/Helper/File.php
patching file app/code/core/Mage/Oauth/Model/Server.php
patching file app/code/core/Mage/Paygate/Model/Authorizenet.php
patching file app/code/core/Mage/Payment/Block/Info/Checkmo.php
patching file app/code/core/Mage/Paypal/Model/Express/Checkout.php
patching file app/code/core/Mage/Paypal/Model/Resource/Payment/Transaction.php
patching file app/code/core/Mage/Sales/Model/Resource/Order/Payment.php
patching file app/code/core/Mage/Sales/Model/Resource/Order/Payment/Transaction.php
patching file app/code/core/Mage/Sales/Model/Resource/Quote/Payment.php
patching file app/code/core/Mage/Sales/Model/Resource/Recurring/Profile.php
patching file app/code/core/Mage/Uploader/Block/Abstract.php
patching file app/code/core/Mage/Uploader/Block/Multiple.php
patching file app/code/core/Mage/Uploader/Block/Single.php
patching file app/code/core/Mage/Uploader/Helper/Data.php
patching file app/code/core/Mage/Uploader/Helper/File.php
patching file app/code/core/Mage/Uploader/Model/Config/Abstract.php
patching file app/code/core/Mage/Uploader/Model/Config/Browsebutton.php
patching file app/code/core/Mage/Uploader/Model/Config/Misc.php
patching file app/code/core/Mage/Uploader/Model/Config/Uploader.php
patching file app/code/core/Mage/Uploader/etc/config.xml
patching file app/code/core/Mage/Uploader/etc/jstranslator.xml
patching file app/code/core/Mage/Usa/Model/Shipping/Carrier/Dhl.php
patching file app/code/core/Mage/Usa/Model/Shipping/Carrier/Dhl/International.php
patching file app/code/core/Mage/Usa/Model/Shipping/Carrier/Fedex.php
patching file app/code/core/Mage/Usa/Model/Shipping/Carrier/Ups.php
patching file app/code/core/Mage/Usa/etc/config.xml
patching file app/code/core/Mage/Usa/etc/system.xml
patching file app/code/core/Mage/Wishlist/Helper/Data.php
patching file app/code/core/Mage/Wishlist/controllers/IndexController.php
patching file app/code/core/Mage/XmlConnect/Block/Adminhtml/Mobile/Edit/Tab/Design.php
patching file app/code/core/Mage/XmlConnect/Block/Adminhtml/Mobile/Edit/Tab/Design/Images.php
patching file app/code/core/Mage/XmlConnect/controllers/Adminhtml/MobileController.php
patching file app/design/adminhtml/default/default/layout/cms.xml
patching file app/design/adminhtml/default/default/layout/main.xml
patching file app/design/adminhtml/default/default/layout/xmlconnect.xml
patching file app/design/adminhtml/default/default/template/catalog/product/helper/gallery.phtml
patching file app/design/adminhtml/default/default/template/cms/browser/content/uploader.phtml
patching file app/design/adminhtml/default/default/template/downloadable/product/edit/downloadable.phtml
patching file app/design/adminhtml/default/default/template/downloadable/product/edit/downloadable/links.phtml
patching file app/design/adminhtml/default/default/template/downloadable/product/edit/downloadable/samples.phtml
patching file app/design/adminhtml/default/default/template/media/uploader.phtml
patching file app/design/adminhtml/default/default/template/xmlconnect/edit/tab/design.phtml
patching file app/etc/modules/Mage_All.xml
patching file app/locale/en_US/Mage_Media.csv
patching file app/locale/en_US/Mage_Uploader.csv
patching file downloader/lib/Mage/HTTP/Client/Curl.php
patching file js/lib/uploader/flow.min.js
patching file js/lib/uploader/fusty-flow-factory.js
patching file js/lib/uploader/fusty-flow.js
patching file js/mage/adminhtml/product.js
patching file js/mage/adminhtml/uploader/instance.js
can't find file to patch at input line 5810
Perhaps you used the wrong -p or --strip option?
The text leading up to this was:
--------------------------
|diff --git lib/Unserialize/Parser.php lib/Unserialize/Parser.php
|index 423902a..2c01684 100644
|--- lib/Unserialize/Parser.php
|+++ lib/Unserialize/Parser.php
--------------------------
File to patch: 
Skip this patch? [y] 
Skipping patch.
1 out of 1 hunk ignored
can't find file to patch at input line 5822
Perhaps you used the wrong -p or --strip option?
The text leading up to this was:
--------------------------
|diff --git lib/Unserialize/Reader/Arr.php lib/Unserialize/Reader/Arr.php
|index caa979e..cd37804 100644
|--- lib/Unserialize/Reader/Arr.php
|+++ lib/Unserialize/Reader/Arr.php
--------------------------
File to patch: 
Skip this patch? [y] 
Skipping patch.
1 out of 1 hunk ignored
can't find file to patch at input line 5838
Perhaps you used the wrong -p or --strip option?
The text leading up to this was:
--------------------------
|diff --git lib/Unserialize/Reader/ArrValue.php lib/Unserialize/Reader/ArrValue.php
|index d2a4937..c6c0221 100644
|--- lib/Unserialize/Reader/ArrValue.php
|+++ lib/Unserialize/Reader/ArrValue.php
--------------------------
File to patch: 
Skip this patch? [y] 
Skipping patch.
1 out of 1 hunk ignored
patching file lib/Unserialize/Reader/Null.php
patching file skin/adminhtml/default/default/boxes.css
patching file skin/adminhtml/default/default/media/flex.swf
patching file skin/adminhtml/default/default/media/uploader.swf
patching file skin/adminhtml/default/default/media/uploaderSingle.swf
patching file skin/adminhtml/default/default/xmlconnect/boxes.css

Answer 1

Try to re-download the Magento Core in your current version. Unzip it and overwrite your current core. Now the patch should work without problems.

If changes are made to the core, you can find them and transfer them via a DIFF between the original core and your core.

(Do not forget backup!)

Answer 2

download magento core structure from magento site and same as your current version

I think you have done some modification in this file that's why patch gives you error in that particular file.

and replace this file with core file

Magento_root/lib/Unserialize/Reader/Arr.php

and check http://magereport.com/ for patch detail is your patch applied or not.

Hope this will help you