My wife and I tend to communicate through gtalk and recently the video chat. However, a couple of nights ago her laptop stopped allowing her to invite people to video call.
After realising it was something to do with the flash plugin I installed the latest version and applied all of the updates to no avail.
After a little Googling I found the answer to be the following and I thought I would post it here in case it's useful to anyone else.
Basically, go to your GMail account settings and find the Labs tab. Scroll right down to the bottom and there should be a Lab for Video Chat Enhancements. Click "Enable" for that lab and then save your settings. It worked a treat and she is now back up and running.
This issue seemed to effect both Chrome and Firefox although other people I have read about only seem to be effected if you use Chrome. Either way that solve her problem.