Below is the message description from Top Secret 16.0 Messages Manual TSS0962W MAXUSER EXCEEDED - XREF TABLE FULL - F(facility) J(jobname)
Reason: The cross-reference (XREF) in-core signon table for the multi-user address space job is exhausted. As a result, Accessor Environment Element (ACEE) information is not being stored in the XREF table (and is stored only for the individual terminal session). Without accurate ACEE information in the XREF table, ACEE refresh might not work. Additionally, unless the address space is running as a started task, ACEE storage could be left allocated at address space termination. This message is issued once per address space.
In an IMS control region, the XREF table is limited to 51 entries. When MAXUSER is exceeded during a signon attempt, the product signs off the oldest sign-on user (based on ACEE information), signs on the user who is requesting signon, and issues this message once. After the XREF table becomes full, any user signons allocate the logon storage in 31-bit Common Service Area that will not be recovered until an IPL.
Action: If the multi-user address space is not running as a started task, stop and restart the initiator to reclaim the allocated private storage for user signons. Increase the MASTFAC facility MAXUSER parameter appropriately (based on the number of simultaneous end users who will be signed on to the address space), then recycle the address space job to activate the new parameter.
Note: For the IMS control region, no action is required.
Resolution
The Top Secret MAXUSER parameter is defined in the facility, and controls how many entries are created in the XREF table when the SOLVE:Access region starts. The default recommended value is 3000. The message occurs when this value is exceeded.
In SOLVE:Access, each user - no matter how many sessions they have - counts as one user, while in Top Secret, each of those individual session counts as a user. So even if less than 1000 users logon to SOLVE:Acess, it is possible to exceed the threshhold of 3000 users.
Rule of thumb: If the error is a one-time, or rare occurrence, there is no cause for concern and no changes need to be made; it was a temporary spike in users and the situation cleared soon after. If the message becomes a more common occurrence, say weekly or every few days, it is time to take a look at what is happening and potentially revise the values in Top Secret.
To understand the function of the XREF table, see Top Secret KB 53072 titled "How to proceed when receiving message: TSS0962E MAXUSER EXCEEDED - XREF TABLE FULL - F (facility) J (jobname)?"
Additional Information
Example of a Top Secret display of a facility for SOLVE:Access with MAXUSER coded: