Microsoft KB Archive/169540

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Error Message: Too Many Outstanding Commands


The information in this article applies to:

  • Microsoft Windows 95
  • Microsoft Windows 95 OEM Service Release, versions 2, 2.1
  • Microsoft Windows 98


The Vnetbios.vxd virtual device included with Windows 95 is limited to 38 posted Listens. Some programs that use the NetBIOS Application Programming Interface (API) in Windows 95 may need to post more than 38 Listens. The following error message may be displayed if this is attempted:

Too many outstanding commands.

Note that posting other commands to the NetBIOS interface may also result in this error message. This occurs mostly with asynchronous commands, but may also occur with synchronous commands. As a general rule, a command uses space for one network control block (NCB) in the device's internal buffer. This buffer is separate from, and does not affect, the number of sessions available to NetBIOS.


The Vnetbios.vxd virtual device runs out of internal storage for NCBs when 38 Listens are posted. A key available in the Microsoft Windows 3.11 System.ini file (the "NumHCBs=" line in the [386Enh] section of the file) that allows the internal storage buffer to be expanded is not implemented in Windows 95.


A supported fix for Windows 95 and OEM Service Release 2 that corrects this problem is now available from Microsoft, but has not been fully regression tested and should be applied only to computers experiencing this specific problem. To resolve this problem immediately, contact Microsoft Technical upport to obtain the fix.

For a complete list of Microsoft Technical Support phone numbers and information on support costs, please go to the following address on the World Wide Web:

This fix for Windows 95 and OEM Service Release 2 should have the following file attributes (or later):

   File name     Version    Date      Time     Size
   Vnetbios.vxd  4.00.953   12/16/97  9:53am   27,245 bytes 


Microsoft has confirmed this to be a problem in Microsoft Windows 95 and OEM Service Release 2 (OSR2).

Microsoft has confirmed this to be a problem in Microsoft Windows 98.


After you obtain and install the update, add one of the values listed below for the "NumHCBs=" line in the System.ini file. Note that the number of Listens is not an exact correlate of the value set for the "NumHCBs=" line. This occurs because the Vnetbios.vxd internal command buffer is allocated in pages, rather than the exact value on the "NumHCBs=" line.

   NumHCBs=32      ; this is the default value, yields 38 listens
   ;NumHCBs=41      ; yields up to 77 listens
   ;NumHCBs=80      ; yields up to 117 listens 

NOTE: The semicolon (;) character shown at the beginning of the sample entries begins commented text. Windows 95 ignores all text that follows the semicolon. Include only one of the lines in the System.ini file, and make sure that the leading semicolon has been removed so that the value is used.

Additional query words: netbios NumHCBs maximum listens

Keywords : kberrmsg kbnetwork osr2 win95
Issue type : kbprb
Technology : kbWin95search kbWin98search kbOPKSearch kbWin95 kbWin98 kbWin95OPKOSR2 kbWin95OPKOSR210

Last Reviewed: January 31, 2001
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