Hi Gerd,
I have had problems in the past with passing control references into subVIs. I had these problems because the strict control reference is often incompatible with a non-strict refnum control, or a strict refnum control of the wrong type. For example, if you have a multi-selection listbox, but you try to wire that control reference to a listbox reference associated with a scalar datatype (single-selection), you will get a wiring error.
The easiest solution for these problems is to right-click on the control reference and choose Create > Control. Then, copy this control into your subVI and use it as the subVI input. I think this will solve your class conflict problems.
If this doesn't work right, let me know and we can talk further...attachi
ng a sample LLB that demonstrates the problem would be helpful.
-D