APPC/CPIC Application May Fail When Using Remote APPC LU Name (193988)

SYMPTOMS

An Advanced Program-to-Program Communication (APPC) application may display the following error message when attempting to allocate multiple conversations at the same time:

   primary_rc = AP_COMM_SUBSYSTEM_NOT_LOADED (0xF004)
   secondary_rc = 0xF0000002

A Common Programming Interface for Communications (CPIC) application may receive Error 20, or CM_PRODUCT_SPECIFIC_ERROR.

This error has been observed in the following scenario:

If an APPC application specifies a NULL Local APPC LU alias in TP_STARTED, and a fully qualified Remote APPC LU name (instead of a Remote APPC LU alias) in [MC_]ALLOCATE. Or, if a CPIC application specifies a fully qualified Remote APPC LU name prior to calling CMALLC (Allocate).
If the APPC or CPIC application attempts to allocate up to 10 concurrent requests within a second.
If the APPC or CPIC application is running on an SNA Server Windows NT or Windows 95/98 client machine and there are several SNA Servers in the subdomain, where some of the servers may not be configured to support the Remote LU name being requested.

NOTE: There are many more common scenarios that can cause the above APPC or CPIC return codes. For more information, please see the following Microsoft Knowledge Base articles:

148359 SNA Server APPC Error: F004 AP_COMM_SUBSYSTEM_NOT_LOADED

132720 SNA Server CPIC Allocate Error 20(CM_PRODUCT_SPECIFIC_ERROR)

CAUSE

When an APPC or CPIC application specifies a null Local LU alias, null Remote APPC LU alias, and a fully qualified Remote APPC LU name, the SNA Server client is not optimized to locate the appropriate SNA Server(s), so the SNA client tries all SNA Servers in the subdomain. However, when the application attempts to allocate multiple conversations at the same instant, the SNA client "server resource location" may fail in some cases to try all servers, and return an error to one or more of the allocation requests.

This problem does not occur when the application specifies a Local or Remote APPC LU alias, because the SNA client determines which servers support the request, and only tries those servers. This improvement has been implemented since the release of SNA Server 2.11 Service Pack 2, but did not cover the case where only the fully qualified Remote APPC LU name is specified by the APPC or CPIC application.

RESOLUTION

SNA Server 3.0

To resolve this problem, obtain the latest service pack for SNA Server version 3.0. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

184307 How to Obtain the Latest SNA Server Version 3.0 Service Pack

SNA Server 4.0

Microsoft has confirmed this to be a problem in SNA Server version 4.0 and 4.0 SP1. This problem was corrected in the latest SNA Server version 4.0 U.S. Service Pack. For information on obtaining this Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

   S E R V P A C K