I have been able to fix the issue by changing the connection to use the 32-bit OLE DB provider. So I conclude that it must have been something to do with 32 vs 64 bit providers not working the same way when using QVB. How or why this issue has suddenly surfaced after happily having used 64-bit provider for months, it escapes me... However, if anyone comes across similar performance issues, it may be worth trying the different versions.
I'm glad I am not the only one suffering this. I have reloads set in QMC and running fine then without notice the task were failing. Yet I can run the document of the server using the desktop client and document loads without error.
Same document just one reload uses qvb the other qv. However, qvb fails and same as you Istvan have been using qvb without error previously.
Will try 32-Bit as work around. Just hate not knowing why.
Cheers Tim......you are not alone