ITSSM_sendSessInfo returns "Session not fail-safe"

Dear all,

We upgraded to ITS 6.20 PL20 here with R/3 4.7 and in both IE 6 SP2 and Mozilla Firefox 1.5.0.7 sessions are terminated after a message "Session not fail-safe" appears in the status bar of the browser (the message actually only appears in IE, not in Firefox. Session is terminated all the same though). The usual "Invalid Session

You have tried to use a WWW session that has already been terminated." is displayed.

I've established that the message is triggered by JavaScript FM ITSSM_sendSessInfo, but can't explain why this suddenly happens. ~timeout (60) and ~usertimeout (.1) are fine and never caused a problem in earlier tests.

If someone could point me into the right direction, please.

Kind regards,

Michael Koch