Problem in calling a FM via RFC in IDOC scenario

Hi experts,

I have a file to IDOC scenario in which I call via UDF RFClookup a custom function module with a certain key to retrieve some values from a custom table of ECC.

In DEV and QTY env. it's all ok, XI retrieve the correct record.

In DSP XI retrieve always the first record of the table called by the FM.

It seems like there is some problem in accessing the FM with the key.

Any hints?

Thanks

Fabio