We have a (C#) .Net webservice that's attempting to create a collaborative edit session with Zoho writer. However every time we attempt to post the document content to the Zoho servers and get the document URL back, we get an Internal Server Error. 

This code was working fine previously (about 12 months ago), and obviously the error code is quite ambiguous so doesn't give us much to work with.  The exception is being thrown on HttpWebRequest's GetResponse() call. I can post additional code if that helps.

Many thanks for any help/pointers!

Mike.