Hi Mario,
it is not possible to say what is wrong here from the description. You have to get the parameters right. Also RSADMIN parameter RSDAI_LOOKUP has to be setup correctly (normally to value = 3, but this depends on NLS solution you have). There where also some bugs in the SAP interface, so there might be also some relevant SAP notes for the problem (this depends on your release). In general I suggest you contact your implementation partner for help, they should have some templates / guidelines. We at DataVard have even automated lookup translator to automate the change of lookups, since the translation itself can be a lot of work.
Cheers,
Martin