We have been able to track down the problem. In the current Uniface version (8.4.06 patch D607) we use, there seems to be a problem with one of the MSSQL...

Actual plans are the same.

Both graphical query plans attached...

I have tried that too and that doesn't make any difference...

I omitted al unnecessary fields from the query (to make it as clear as possible). So it's not just adding one field to the index to make it index covered.

Parameter...

Finally found it. The raiserror is in a nested procedure...

No (off course not)...

Any other user activity is just running fine. I can also normally query the database.

My first guess is that it is something within the procedure, but I...