IKT00201I

Explanation
TSO issues this message when a logon to TSO fails
because it exceeded the maximum number of TSO users allowed on the
system.

System action
Processing continues.

Operator response
If you want to temporarily allow more users
to log on to TSO concurrently, issue the system MODIFY command. If
the maximum allowed users should be changed permanently, contact the
system programmer.  
See Modifying TSO/VTAM
Time Sharing in z/OS MVS System Commands.  

System programmer response
If you want to permanently allow more
users to log on to TSO concurrently, update the USERMAX parameter
in the system parmlib member, TSOKEY00.
See  Statements/parameters
for TSOKEY00 in z/OS MVS Initialization and Tuning Reference. 

User response
If your user ID is in a disconnect state, you
can attempt to logon again using LOGON user ID RECONNECT. If your
logon attempts continue to fail, contact the operator.

Problem determination
Not applicable.

Source
z/OS® Communications
Server VTAM®: TSO/VTAM

Example
 IKT00201I MAXIMUM USERS LOGGED ON, TRY LATER