If you are running Microsoft Dynamics CRM 4.0 and receiving the error, “Authentication to Microsoft Dynamics CRM server could not be established” then you will want to try the following fix below. There could be a couple reasons you are receiving that error. Here is just one way to fix it.
In this instance the user had recently changed his password. Suddenly he was receiving an error that the CRM client wouldn’t launch with Outlook and browsing to the CRM website would result in an authentication popup window.
Microsoft Dynamics CRM Server
Browse to your Control Panel.
Click on “User Accounts.”
Under the “Credential Manager” click on “Manage Windows credentials.”
You will most likely have an entry for your CRM server (picture example shows Outlook entry). Click on the drop down arrow and then click “Remove.” This will clear out the cached credentials to your CRM server and allow the user with the recently changed password to now connect to CRM, both via Outlook and with Internet Explorer.