By the way, I did work around this problem replacing the ITVF with store procedures, I don't know exactly way, but talking about performance, it's better a sp. I could use a lot of nested sp and make a more DRY design. I think maybe its because in the sp I can use temporary tables that use less memory and the SQL Server can make a better execution plan. The disadvantage is that sp are a bit more dificult to write and less maintainable than ITVF's