Yesterday i got a call from client to know about the active users of our siebel appliaction. We have three ways to get details of active users in siebel.
1. Go to Server Administration > Servers > Object Manager For the desired OM , We have COMPONENTS in below list applet There you can find Session and TASK for them In Session you can get active users. 
 

 
 2.  You can also find information by running _stats.swe i.e. running stats on the web server if stats collection is enabled on the web server and session …

Symptom or Error Message
The Transaction Router Siebel Remote server task may fail under certain conditions which will cause a backlog in the transactions to be routed to Siebel Remote mobile users and regional nodes. Symptoms of a Transaction Router failure are usually an error on the Status field on the Server task applet, and the Task State field would report that the task has exited with an error:
Task State: Exited with error
Status: ERROR: 1 client(s) failed with errors, 0 client(s) successful
To generate more detailed trace information:
            • In Siebel …

                           UNDO CHECK OUT: Is the process of reverting back the changes that you have done and also unlocking the object on server. So, two things happen when you do an UNDO CHECK OUT.