Hi Jens
I think the plain HTTP adapter had a limitation of having 6 parameters in the dynamic URL part. From the link below, I think HTTP_AAE inherited the same limitation.
Configuring the Java HTTP Adapter on the Receiver Channel - Advanced Adapter Engine - SAP Library
Your system is just 2 SPs away from being able to support the new REST adapter. I'd give the same recommendation as I gave in the thread below - try and upgrade to get REST as it is superior in HTTP scenarios.
Re: Dynamic URL in HTTP_AAE PO 7.40
Rgds
Eng Swee