Symptoms
An application exception (trap) occurs in the SNA Server service(SNASERVR.EXE) when used with the Attachmate Extra! 3270 version 4.xemulator.
If you have Dr. Watson (DRWTSN32.EXE) configured as the default debugger,the DRWTSN32.LOG shows an exception similar to the following:

Application exception occurred:
App: snaservr.DBG (pid=147)
When: 8/1/1995 @ 16:39:1.590
Exception number: c0000005 (access violation)In addition, SNA Server logs Event 624 in the Windows NT Application Log(as seen in the Event Viewer) when this trap occurs. The following is adetailed description of the Event 624 that is logged when this trap occurs:

Creating dump file C:\SNA\TRACES\SNADUMP.LOG for SNASERVR.EXE
EXPLANATION
A process (SNASERVR.EXE) ended abnormally due to a protection
violation or similar condition and a dump file SNADUMP.LOG has been
created that contains information about the state of the process at
the time of the exception. Register information is contained in your
Windows NT root directory in the file DRWTSN32.LOG.
Resolution
A 3270 emulator has two connections to the SNA Server service. Oneconnection is for SSCP-LU data and the other one is for PLU-SLU (PrimaryLogical Unit – Secondary Logical Unit) data. The SNA Server service trap iscaused because the 3270 emulator is sending a PLU-SLU message on theconnection that is only meant to handle SSCP-LU data. This is behaviorwhich the SNA Server service is not expecting, and it traps when itaccesses its session control block for the SSCP-LU session and treats it asa control block for the PLU-SLU session.