We had this problem and Edxcel were very unclear. they just said it was a flash problem.
The problem is definitely to do with the workstation. I have an exam1 user locked down with GP. They can't do anything with the account except run the 'Promissor' software. We also run IE7.
Every time we have a problem to do with the graphics it's to do with the permissions on the C:\Program Files\Promissor folder.