The odd thing is it doesn't happen all the time, more like every second or third time I attempt to launch Photo Viewer by double-clicking on any image. Similarly, I'm getting frequent DWM crashes when testing the problematic themes using WSB (for example, when making changes and then testing to see the changes) and occasionally when performing any GDI intensive tasks such as launching standard Windows UI applications like MS Office Outlook 2010, though such occurrences are far less frequent and less consistent. Again, in this scenario the crash does not happen consistently but often enough to see a pattern.
At first I thought perhaps it was caused by the background color used in my theme as well as the other problematic theme for Photo Viewer (black and dark grey), however changing the appropriate values to their defaults did not resolve the issue with Photo Viewer (though it did cause images to load more quickly).
The third party theme in question is the one referenced here (I only applied the shell theme extracted manually from the installer, I did not use any pre-built themepacks or any third party executables):
https://www.youtube.com/watch?v=n2V-gir2p_wMy only conclusion now is that perhaps one of the modifications that theme (and thus my own theme which is based on it) makes to the system causes some type of GDI overload and/or corruption or race condition leading to these errors/crashes.
If you require a copy of my theme for analysis just let me know and I will provide it.
Thanks