Hi,
Just an idea, what if instead of logout/login you would start lxpanel from a (user) console, this way :
$ lxpanel
(no &, in order to see if something special comes out in the console). And by the way, when the panel crashes, you would display the content of the file ~/.xsession-errors and copy it's full output here, it might help find out what is going on.
Regards,
Mélodie