hi,
1. what version , sp and patch are you using?
2. have you tried searching this forum, the wider internet, or indeed www.service.sap.com/notes with the keywords "WIH 00013 invalid session" ? what solution or notes have you evaluated?
3. what reparative steps have you taken thus far to try to resolve it? please call out the changes made.
4. have you identified systematic workflow that reliably reproduces this problem? what is it?
regards,
H