Error 17066

In the last week we are seeing several occurrences of the following error:
Error 602, Severity 21, State 30:
Could not find an entry for table or index with partitionID 189907171868672 in database 2.

This is always followed by a stack dump and this error:
SQL Server Assertion: File: <qxcntxt.cpp>, line = 1069 Failed Assertion = 'cref == 0'.

I have run checkdb on tempdb and no errors are reported. Additionally, we have dropped and recreated the sp indicated in the stack dump. The errors continue.

We are running 64 bit SQL 2005 with sp2.

HELP!!!!!!!!!!!!!!!!!!!!!!!!!!

Stack dump normally means a bug in sqlserver. It's best to contact PSS to get it resolved.