Another hit for Jason Jones and Jim Harrison!
“Think this is sorted now.
I needed to disable the “apply session timeout to non-browser clients” in the advanced form options for the web listener that was shared for OWA and ActiveSync. If you follow the built-in wizards, this option is disabled by default for any listener that is selected for ActiveSync use – that’ll teach me! 
Thanks to Jim Harrison for the pointers!
“You don’t want the FBA timeout applied to EAS clients.
The folks in Exch, WM6 and ISA all agreed that a wide-open 30-minute timeout was good for battery life. If you close that sooner, the client has to re-authenticate.” “
So there you go — those wizards do bear magic!
For the complete thread, go here:
http://forums.isaserver.org/m_2002045198/mpage_1/key_/tm.htm#2002053976
HTH,
Tom
Thomas W Shinder, M.D.
Site: www.isaserver.org
Blog: http://blogs.isaserver.org/shinder/
Book: http://tinyurl.com/3xqb7
Email: [email protected]
MVP — Microsoft Firewalls (ISA)