cause is
This issue may occur if the following conditions are true: • This issue may occur if the client computer submits simultaneous, long-term requests against a file server that uses the Server Message Block (SMB) protocol. An example of a long-term request is when a client computer uses the FindFirstChangeNotification function to monitor a server share for changes.
• This issue may occur if the MaxCmds registry value setting on the client is less than 50, or the MaxMpxCt registry value setting on the server is less than 50.
Note The MaxMpxCt registry value setting may have a different name on other SMB/CIFS implementations. The Common Internet File System (CIFS) specification refers to it as MaxMpxCount.
Resoultion :
Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.
To resolve this issue, verify that the MaxCmds and MaxMpxCt registry values are set to 50 or more. To do this, follow these steps:1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click the following key in the registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\lanmanworkstation\parameters
3. In the right pane, double-click the MaxCmds value.
4. In the Value data box, verify that the value is 50 or more.
Note In a Microsoft Windows Terminal Services environment, you may have to set the MaxCmds registry value to 500 or more. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
232476 (http://support.microsoft.com/kb/232476/) Terminal Server client connections and logon limited by MaxWorkItem and MaxMpxCt values
5. Locate and then click the following key in the registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\lanmanserver\parameters
Note Make sure that you make this change to the lanmanserver\parameters registry key and not to the lanmanworkstation\parameters registry key mentioned in step 2.
6. In the right-pane, double-click the MaxMpxCt value.
Note On SMB servers that are running a version of Windows earlier than Windows 2000, the MaxMpxCt registry entry is named MaxMpxCount, but has the same function.
7. In the Value data box, verify that the value is 50 or more.
Note The MaxMpxCt value determines the maximum number of simultaneous, active requests that the server permits from an individual client.
8. Quit Registry Editor.
Note The MaxCmds and MaxMpxCt registry entries are REG_DWORD decimal entries. If they do not exist on your computer, you can create them as new REG_DWORD values. The range of values for these registry entries is between 0 and 65535.
see the support website of Microsoft
http://support.microsoft.com/kb/810886