CFReport Error

Any idea what would cause this error in ColdFusion 8?
Could not initialize class coldfusion.runtime.report.Report

I am running a very simple test script containing<cfreport template="reports/avery_5160.cfr" format="pdf"> which runs fine on CFMX 7, but in CF 8 I just get the initialization error. (We are running Enterprise edition with sandbox security enabled, on Windows Server 2003.)

Thanks!