Code 415: Unsupported media type

Hi

I got the error code 415 Unsupported Media Type, when I try to Post in transaction /WFND/GW_CLIENT

My procedure is:

1. I use the HTTP method GET data from a one order
2. press "Use as Request"
3. change the HTTP method to POST
4. Execute

Now the error Code 415: "Unsupported media type" and the message "The server is refusing to process the request because the entity has a unsupported format"

Anyone who can help me?

Thanks

Aikon