The OCX, and Crystal Reports 8.5 have been gone for a very long time. SQL Server 2008 came out well after the retirement of both CR8.5 and the OCX. If your VB6/OCX application was working with SQL Server 2000, and now it's not working with SQL Server 2008 then it's more likely that the database drivers aren't recognizing some change from SQL Server 2000 to SQL Server 2008.
The fact that you say about the rpt is working in CR ide and not when is called from the VB6 app tells me that the problem is in the OCX
I would recomend to upgrade your code to RDC and if it's possible to a newer version of CR