Without more systems information, the first thing that comes to mind is that it might be a crossdomain issue.
If it is, you can find plenty of information on adobe.com in reference to that.
Let me know if you have more information but if it works in one browser, should work in all.
i have the same thing happening. I have a person with two laptops both using firefox, on one laptop the swf functions as desired on the other there is a security error ( not a sandbox error - just a "security error") It is not a cross domain issue - which seems to be everyone's favorite suggestion, since the swf resides on the same server/domain its calling
here is a similar issue http://bugs.adobe.com/jira/browse/FP-2264
in my case 10.0.12.36 version consistently produces the desired result where as 10.0 r32 has issues.
It is not a cross domain issue since it uses relative referencing to make the xmlhttp request call. It is also not a security issue.
The user did seem to have quite a few Adobe authoring type tools open. Does anyone know if there could be some kind of conflict with other Adobe services running at the same time?