Problems with dinamic web services

Hello

I’m trying to make a connection between Oracle Siebel and Biztalk, Siebel use a dinamic URL and have a log time limit of 10 minutes so i decide to log and logout once and again with a C# library, this works fine until Biztalk sends the message: “The remote server returned an error: (500) Internal Server Error” and then it close the orchestration and i need to restart the orchestration again, can you help me with this issue, thanks.