OpenPS for MS Project issue

Hi experts,

I have the following issue:

When I try to connect to the SAP System my MS Project shows "Logon in process - please wait..."

but nothing happens even after waiting a longer time.

Im running MS Project 2007 Standard and have installed OpenPS 4.0 PL 4

The error_log gives me this information:

Error Number       = 91

Error Description  = Object reference not set to an instance of an object.

Error stack Trace  =    at OPenPS_BackEnd_Adapter.OPEN_PS_BACKEND_ADAPTER.GetInstance(Connection& destination, Boolean UseBWRFC)

Error Help File    =

Has anyone an idea how i can fix this?

Thanks

Pascal