Classification of sales order (VBAK) with CLFM_OBJECT_CLASSIFICATION

Hello all,

how can I access the classification FM CLFM_OBJECT_CLASSIFICATION (transaction CL20N) from within a sales order?

I tried to execute the FM within the exit USEREXIT_CHECK_VBAK while using a button created by GuiXT. The problem is, that I can't reset the OK-Code which I have to set for the button. Therefor the system tells me via error message, that the OK-Code xxxx is not allowed.

Do you know any other possibilities to execute the classification FM through the creation/modification of a sales order?

One more thing: While creating a sales order, the order doesn't have an order number yet, so I can't execute the classifcation. This means, I have to post the order to get an order number and do the classification afterwards (VA02).

Any suggestions concerning that point?

If any of you has any suggestions, I would be quite happy.

Thanks in advance.

Harald