Outlook 2010 - Username Password

I have 6 users in a branch office
There is a VPN connection between our offices.
Our exchange 2010 server is hosted in our head office

The branch office computers are installed with Office 2010, they are connected to the domain.

Randomly, since Thursday Outlook has been persistently requesting these users to enter their username and password.

Their user accounts are not disabled, the passwords have not expired, the VPN is on and working.

They have restarted their computers, I have restarted their local DC but the issue is still occurring. I have also deleted and re-created user profiles in Outlook to no avail.

DC is Windows Server 2008 R2,
Exchange is 2010 SP2 on Server 2008 R2

Does anyone know what could be causing this?
Who is Participating?
netcmhConnect With a Mentor Commented:
So, what changed since Wednesday-Thursday? Were patches put in? Did traffic go up? Is there some particular job which ran? Backups? What is the link and speed between the 2?

Is their local DC in sync with yours? Did you run a dcdiag? GPO updates? Did you run a gpresult?

Can you put a laptop with wireshark in between any one of those computers and your VPN?
antoniokingAuthor Commented:
Hi netcmh

dcdiag passed all tests but one. DFSREvent.
repadmin /showreps shows all last attempts as successful.

It may have been recently installed patches, I'll check that shortly.
Please ensure that you can ping between the DCs with ip addresses, computer names and FQDNs. Is there a firewall blocking AD replication traffic?

Can you access the sysvol and netlogon folders on either end from the other?

Are the subnets correct on Sites and Services?
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antoniokingConnect With a Mentor Author Commented:
I have just remembered something that we have changed via Group Policy...
Internet Proxy settings.

Disabling these settings resolves the issues.

Now I know the cause I can investigate it further
antoniokingAuthor Commented:
Unforunately the issue has returned.
Proxy settings are off, HTTP is off, but Outlook is still requesting a username and password.
Are the clients windows 7?

Control Panel>User Accounts>Manage your credentials>Delete everything in here

And, can you verify that the accounts are not locked out?
If that doesn't work, try changing the Logon security to negotiate authentication

On the client, Exchange account>change>More Settings>Connections>Uncheck Connect to Microsoft Exchange using HTTP>Apply
Same window, go to Security>Logon network Security>Negotiate Authentication>OK

Leave the client running for few minutes, then exit Outlook and try reopening Outlook.
antoniokingAuthor Commented:
Hi netcmh
Nothing stored in Credential Manager
HTTP is already off and logon security is already set to negotiate.
antoniokingAuthor Commented:
Thanks netcmh, asking what had changed made me think.

Adding proxy settings to that office caused the issue with outlook.
Switching off "On slow networks, connect using HTTP first, then connect using TCP/IP" in Outlook resolved the problem so we can still use our proxy filter.

I would recommend to anyone reading that they set their proxy filter to allow the Outlook HTTP traffic to pass through the proxy.
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