I am getting this same error when in Mame, not PC games. The log shows it as an "Error 53 File not found in CTRLR_ActivateEvent".
I use 5 as my "next emulator" button on my cp and I get this error when 5 is pressed. It was working great for over a month and i haven't changed anything. Strange.
If this is something that will be fixed in v1.6, I can wait.

Thanks!