I think that issue is caused by the whitelist feature that was added with this patch.
If you need to fix this on 1 instance and you have shell access to it you can use this - https://github.com/rhoerr/supee-6788-toolbox
If you have only ftp access, need it applied on multiple environments and the only thing that needs to be updated is whitelist db you can use this - http://supee6788.magebit.com
Hope this helps.