MIgrating to weblogic 10

Hi,

As part of weblogic migration from weblogic 6.1sp3 to weblogic 10.
an application which containsa servlet is deployed as a war file. There is
client executable invoking this servlet from client PC. Presently this is
working fine in weblogic 6.1 sp3.
Now we are trying to migrate this to weblogic 10. we deployed the war file as it
is to weblogic 10. but when we try to invoke the servlet from the client
executable, its not even reaching the servlet.

Note: client exe is trying to execute the servlet on host name and port basis.
we dont have the source code of the client executable.. 
We also tried to deploy the same in weblogic 8.1 and its working file. But we
are facing probelm while deploying in weblogic 9.x and 10.x.
Are there any special security that should be taken care in new versions i.e.,
9.x,10.x when compared to before versions in case of web application(warfile)
deployment.
ANyone please help. Iam not getting any suggestions from this forum. I dont know
Y.
Please let me know if any one need more info abt this.