Windows Server 2003 supports 1024 sessions to pipe\samr that use different security contexts, whereas Windows 2000 supported 2048 sessions. When the limit is exceeded, the server returns a STATUS_INSUFFICIENT_RESOURCES error.
Normally, a pipe is only open for a short duration, but if the client doesn't send a close request, you may reach this limit.
To workaround this behavior, you can close the open open sessions by running, or scheduling, the following batch:
for /f "Tokens=1" %%f in ('net files ^| findstr /i /l /c:pipe\samr') do @net file %%f /close