Exchange/outlook error reaching remote server

I have a client who is getting an error message in Outlook when trying to reach the Exchange server. Both Outlook and Exchange are version 2010. Attached is the exact error message.

Only one user is receiving this. He connects to Exchange over a site to site VPN tunnel and no changes have been made with the tunnel/firewall configuration to my knowledge.

Google turns up nothing. :) Any advice?
LVL 10
Schuyler DorseyAsked:
Who is Participating?

[Webinar] Streamline your web hosting managementRegister Today

aa-denverConnect With a Mentor Commented:
Here is an article that references the error.  It is a .Net related error. Causes and solutions are offered.  If other clients can connect over the same VPN connection, then it could be that a software update is needed.  Is the client's computer up to date with Microsoft updates, particularly .NET?
Trenton KnewOwner / Computer WhispererCommented:
I would suspect a firewall dropping the connection.
James HIT DirectorCommented:
If you look at the firewall logs when he is connected, do you see any traffic that is being denied or not routing back through the connection. Seems like Outlook isn't getting a response from Exchange and throwing that strange error.
Schuyler DorseyAuthor Commented:
It ended up being an Outlook Add-in that was causing the error. Thanks for all of your help!
All Courses

From novice to tech pro — start learning today.