Urgent...please Help Asap.....!!!!!!

[astrixsun]

hi all,
I am a programmer analyst n m new to this forums.
I made a mobile application using WML for client and ASP as the server scripting language.I have tested the application and its working perfectly on Openwave simulator.I basically hard coded our wap gateway address on the simulator.
The problem is that is our client is not able to run his application on Nextel phones.He even tried connecting to the Nextel servers using Openwave Simulator on his side but to no use.
The strange thing is that when he runs the application on Singular network, it works perfectly, but on his Nextel phones he gets error "Http 500 Error".
I've been to other forums n all have told me about the poor nextel network and suggested me to change network.But am afraid I cant do that so "Some one can please tell me a solution of how to run this application on Nextel phones" or "What possibly is causing this problem".

Thanks in advance.