Please check this post: Security Patch SUPEE-9767 - Possible issues?
For image upload errors read this:
Image Upload callback
The image gallery controller has been updated to add a validation callback.
What to do
If you're using a custom module that does image upload with code that looks like this:
$uploader = new Mage_Core_Model_File_Uploader('image');
$uploader->setAllowedExtensions(array('jpg','jpeg','gif','png'));
$uploader->addValidateCallback('catalog_product_image',
Mage::helper('catalog/image'), 'validateUploadFile');
$uploader->setAllowRenameFiles(true);
$uploader->setFilesDispersion(true);
I strongly suggest you update that code by adding the following piece after it:
$uploader->addValidateCallback(
Mage_Core_Model_File_Validator_Image::NAME,
Mage::getModel('core/file_validator_image'),
'validate'
);