Not knowing too much about this, I think I can at least steer you in the right direction.
I read about this a while ago and if my memory serves me correctly, it has to do with the codec that Camtasia uses when creating the avi. file. I actually had to go to their web site (to many Bud Lights) to look it up and they use a codec called “TSCC”. If one computer composes that AVI file and then another computer tries to open it, unless that computer has that “TSCC” codec it will look all messed up.
Go to their and you might fine more info.
http://www.techsmith.com/camtasia.asp
The link below however takes you to where I think you might find an answer.
http://techsmith.custhelp.com/cgi-bin/techsmith.cfg/php/enduser/std_adp.php?p_faqid=154&p_created=1104264463&p_sid=-8NF1G
