Error connecting JCO.Client

Hello!

I've got a little problem with Adaptive RFC calls: After exactly 10 times executing my call I always get the following Exception:

com.sap.tc.webdynpro.modelimpl.dynamicrfc.WDDynamicRFCExecuteException: Error connecting using JCO.Client: null

Has anybody by any chance got an idea why or how to handle this problem?

Thank you very much in advance!

Best Regards