Approver has got no list of Travel Requests in ESS but he does in WF-Inbox

Hi Experts,

I've implemented Travel Management ESS-Szenarios (WD4A) in our portal. One is FITV_POWL_APPROVER; it should supposedly show workitems which have been put in the respective user's inbox via workflow (WS20000050 is used) e.g. for Travel-Requests. However, no entries are shown. I checked the Approver's inbox and the workitems i expected to show up in ESS are there... The Backend works as it is supposed to be but the WD simply can't display that...for some reason. What could be the possible cause for this?

System Information: ECC ERP 6.0 with EHP 4 SP Level 30.

Tell me if you need more technical information about our system.

regards, Lukas