A long time ago i ran into a problem where Windows Server 2008 R2 loses the ability to connect to a network share on a Windows Server 2003.

Microsoft has now finally released a hotfix to the problem (KB2194664).

When the Windows Server 2008 R2 is restarted everything is working as it should. But after a while it can no longer connect to a network drive on a Windows Server 2003 server.

Sometimes I cannot map on the UNC name and sometimes I cannot map on the IP address. 

When I cannot map the home drive on the UNC name I will get the following error:
System error 53 has occurred. "The network path was not found"

When I cannot map the home drive using the IP address I will get the following error:
System error 59 has occurred. "An unexpected network error occurred."

Back in January 2010 I started a tread on the MS forum describing the problem. It has now grown to be a large tread with 159 posts and over 16.000 views.

The tread can be found her: http://social.technet.microsoft.com/Forums/en-US/windowsserver2008r2networking/thread/9f93508c-71fa-4807-b41a-8f558563afe3

I and several others from the thread opened a case at Microsoft and now Microsoft have finally released a hotfix to solve the problem.

Microsoft's description of the problem and the hotfix can be found at http://support.microsoft.com/kb/2194664

Sadly MS have made the forum read only so the original tread cannot be updated with info about the hotfix.

GrandmasterPhil has created a followup thread on the problem where I also have posted a link to the hotfix: http://social.technet.microsoft.com/Forums/en-US/winserverNIS/thread/9863df3c-4c15-4b19-8068-19572514a0f4

Thanks

Thomas