Microsoft KB Archive/168815

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Knowledge Base

Article ID: 168815

Article Last Modified on 10/28/2006


  • Microsoft Exchange Server 4.0 Standard Edition
  • Microsoft Exchange Server 5.0 Standard Edition

This article was previously published under Q168815

IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information on how to do this, view the "Restoring the Registry" online Help topic in Regedit.exe or the "Restoring a Registry Key" online Help topic in Regedt32.exe.


The Microsoft Exchange Server message transfer agent (MTA) may not start; one or both of the following event ID's will be seen in the event viewer:

   Event ID: 9228
   Source: MSExchangeMTA
   Type: ERROR
   Category: Configuration

   A fatal resource limit was reached while attempting to open an
   association. The number of network type 2 listen control blocks
   requested is too high. Number requested: 2. Number configured: 1. [BASE
   IL MAIN BASE 1 250] (16)

   Event ID: 4300
   Source: MSExchangeMTA
   Type: ERROR
   Category: Configuration

   Unable to initialize due to a bad configuration. Contact Microsoft
   Product Support Services. Error code=%1 [%2 %3 %4 %5] (16)


This is caused by an inadequate number of control blocks allocated to a transport stack. In the above error message, the "network type 2" refers to TP4 protocol. Two control blocks were requested; however, there is one allocated control blocks. The content of this error message may vary, dependent on the mis-configured control blocks for the network type.

   Network Types    Numbers

   Type     0x01    TCP/IP RFC 1006
   Type     0x02    TP4
   Type     0x03    Eicon X.25
   Type     0x04    Named pipes over RAS connection
   Type     0x05    RPC


WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall Windows. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys And Values" online Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" online Help topics in Regedt32.exe. Note that you should back up the registry before you edit it.

To correct the problem, do the following:

  1. Start Windows NT registry editor (Regedit or regedt32).
  2. Modify the following value to 0x2

          \MSExchangeMTA\Parameters\TP4 control blocks: Value 0x2

There must be at least two control blocks allocated to TP4 in the registry. This is true regardless of whether TP4 protocol is used or installed on the server.

The default registry value for TP4 is 0x14H or 20 Decimal.


For information about the limit on the number of allowed socket control blocks for TCP and TP4, please see the following article in the Microsoft Knowledge Base:

166602 XCON: MTA Only AllowS 64 TCP/IP or TP4 Connections

Additional query words: resource Xcon

Keywords: kbusage KB168815