Makes sense that you'll have issues, CR 8.5 predates 2003 TS.
By compiled reports I assume that you mean those reports which were compiled using the Crystal compiler, not a 3rd party application.
Saying sometimes works is pretty vague, do you receive an error, a blank screen, or? Please try to convey basic information in your reports.
There were known issues with the compiler in XT sometimes, changing the compatibility mode for the programs to Windows 2000 did the trick.
-k