Problem with HTTP query string(Urgent help reqd)

I am using WAP Access point to make a GET request to URI:
http://mysever/webapp/somejsp.jsp?data=xyz&User-Agent=me

somejsp.jsp take this data and logs it and returns empty body.
Prob is when i invoke this request no logging happens and i get
HTTP 502 i.e. bad gateway (and sometimes HTTP 500 i.e. internal error) on the client side


But when i invoke GET request to URI:
http://myserver/webapp/somefile.txt
I am able to retrieve whole of somefile.txt

Could somebody please help me.

Regards
Abhinav