This event is due to overwhelming request on a Windows server that it cannot handle. In some cases, the system locks up and the only way to get to it is to reboot. You need to make a registry entry for MaxWorkItems. Always check Microsoft Technet for this kind of issues. Using regedit, go to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters, right click, choose New, click DWORD Value and enter "MaxWorkItems". Double click it and choose decimal under the Base option, and put a value data between 1 and 65535. Microsoft advices using 4096 and doubling this value until the server's WorkItemShortage is below 3 (this can be monitored with Microsoft performance monitor Server\WorkItemShortage).
Note: Registry modification is at your own risk. Always backup your registry before making any changes to it.