Hi chikaboo
Thank you for your post. Firstly please be sure that you have installed the latest version that is 1.6.912.18, and available at the link below:
http://www.solveigmm.com/?Products&id=AVITrimmer#Download
If it is the last one, please make a new test, when you get an error, just close the trimmer and try to open this file in a new instance.
Thank you for your help.