Make a backup copy of im.jnlp.
Open the im.jnlp Instant Messenger resource file in a text editor.
Search for the line:
Add the following argument to the end of the section:
Where type is one of ALL, API, XMPPTRAFFIC, or CLIENT. See Instant Messenger Log File Content Options for details.
Save and close the im.jnlp file.
If you are using Sun Java System Application Server or Sun Java System Web Server, redeploy the resource files as described in Redeploying Resource Files.
Relaunch Instant Messenger.
Locate the log file.
By default the log file is stored as usr_home/.sunmsgr/messenger.log.
You should revert back to the backup copy of im.jnlp when you have finished troubleshooting Instant Messenger. Then, redeploy the resource files as described in Redeploying Resource Files.