It crashes because I can almost guarantee they are using the same folder to store videos/screenshots with other apps that do the same thing (Raptr/OBS/Afterburner/Dxtory/Fraps etc..) the problem arises when those programs use a container that Action! doesn't like. Well what happens is, action fires up goes to display the thumbnails of those video/images has a conniption fit because it doesn't like those files and crashes. Solution empty those folders you have action! pointed to or have it point somewhere else. Your welcome.
Example:
Action set to store videos in C://Video
Afterburner set to store videos in C://Video
You decide to use Afterburner to record a video using it's VCE h.264 codec, and since it only works with the .MKV container you encode using the mkv container
Later on you decide to open Action!, and bam crash. It doesn't like that video using the mkv container from Afterburner in there.
Hope that explains it for ya, mirillis so you can implement a fix or post this solution as temporary fix,