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');
I strongly suggest you update that code by adding the following piece after it: