@GaryFeldman - Awhile back on a similar post from you (maybe for same client), I mentioned doing a Process Monitor trace at the time the 8900 error occurs in FRx -
http://technet.microsoft.com/en-us/sysinternals/bb896645
Then in Process Monitor, start the trace and create the scenario that causes the 8900 to appear (or whatever error or issue is occurring on screen). Then you save trace to CSV file, open in Excel, and sort by Result column, then Time of Day column. You may see an ACCESS DENIED error which will show you which registry key or file/folder the permissions issue occurred on.