Here is the info from the help screen:
Displaying Session Status
webMethods Mainframe Administrator reports status information for each session. Valid entries for the Status column of the HostPool Detail screen are shown here.
The session is currently not started. To start, click No in the Started column. Yes appears when the session starts.
The session is currently active and connected to a host application region, but no transactions are currently being processed.
The session is currently active and connected to a host application region, and a transaction is currently being processed.
The session is currently starting or stopping the connection to the host system.
Pending SignOn/ SignOff
The session is currently processing a SignOn or SignOff handshake with the configured host application region.
The session has been disconnected from, or failed to establish a connection to, the desire host application region. Refer to webMethods Mainframe event log for more information about the error.
The session is currently owned by an application program that issued either a LockSession or SmartLock .
webMethods Mainframe has validated the connection to the mainframe, but the session has not been able to connect to the host application region. If this problem continues, take a session trace and contact webMethods Customer Support.
The supplied Sign On information (User ID and Password) was not validated by the host application region. Ask your IT department to verify a valid User ID/Password combination for this host application region.
LU Configuration Error
The session has been connected to a host application region, but the SNA BIND information was for the wrong type (for example, the region received LU2 BIND but the session was configured for LU 0). Check that the host connection pool definition and the host resource definition match.
webMethods Mainframe is currently processing a shutdown. All of the sessions are being disconnected from the host system.
Host Tx Timeout
A transaction was being processed on this session, but the host system failed to respond within the configured amount of time. Power the session off and on to recover this status. Consult with your IT department about any mainframe problems during this time.
Host Tx Error
A transaction was being processed on this session, but a protocol or configuration violation was encountered. A common reason for this error is a conversation transaction that has not been configured correctly. Power the session off and on to recover this status. Check the webMethods Mainframe event log to find the specific error that occurred.