Dynamically Populate a DropDown using VRO Actions

I am very new to the whole vRealize Automation Ochestrator environment. 

One of the first things i would like to achieve during our POC is to dynamcally populate dropdown properties. 

I have created simple little VCO Actions, to feed back data to VRA, when i choose one of this Actions via a Property VRA throws an Error: 

Error while saving proverty definition: System exception

I struggle with getting around this issue, since all the registrations are working and all the communication otherwise works fine, all the components are in the same subnet as well, so no FW in between.

I have attached the part of the catalina.out log which is being produced during the failed saving request. 

I am gratefull for any help. 

thanks

B