May be will help someone.

Suppose you have Windows 7, Windows 8 and Windows XP or Windows Home Server PCs and multiple shares. All works.

Suddenly you have situation where Windows XP / WHS computers do not see or can't connect to specific computer (Windows 7/8) shares. Error states that you do not have credentials (all other OSs work perfectly with same computer still). And all worked for long time perfectly.

Go to your Windows 7/8 PC that reject connection. Run Eventvwr.msc, check for errors messages. Look for "The server was unable to allocate from the system nonpaged pool because the server reached the configured limit for nonpaged pool allocations."

Now check that it is issue caused by memory problems in Server service. Run services.msc. Stop Server service, and after stopping run it back on (you could need to run also Computer Browser service). After you do it usually things go back to normal (as it is internal memory allocation issue and restarting get rid of almost all previously allocated memory).

To prevent it happening again, you need to run RegEdit (on affected Windows 7/8 machine) .

Set

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\LargeSystemCache

equal to 1. And

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\lanmanserver\parameters\size

equal to 3.