HTTPReceive & Internal Server Error (500)

Dears,

We have an application that contains orchestrations that receive message using BTSHttpReceive.dll file. We have created virtual directory for BTSHttpReceive, and there is a web application that receives messages from 3rd party and forward it to BTSHttpReceive virtual directory. Everything was running fine. However, lately, in the web application logging we receive “The remote server returned an error: Internal Server Error (500) ProtocolError”

If we do an iisreset, or restart for the server, everything goes fine again, however for around 24 hours more or less. Till now I cant figure out why this problem happen.

Please advice,

Thanks in advance,