Can't delete files from within an App

Hello,
I use an image viewer called Xee to quickly browse photos. However, recently for reasons unknown to me, I can not delete files from within the app any more. If I press the delete key, I just get an error message that it can not happen.

I have administrator rights, and I can delete the files from Finder, but this is too much work to get out of Xee and find the right file in Finder.

Xee used to delete absolutely fine in the past.

The files are on a folder on the Mac's 2nd HD and I am running the latest version of OSX.

I'm not familiar with that particular app so can't help with it internally, however, have you checked permissions for the folder the files are in, and likewise permissions for the second hard drive?

Also, is the image viewer "Xee" up to date and compatible with Mountain Lion?