When I press save after editing an post i get this error:
An error has occured!
Unable to load the 'main' template
And this box openes:

Using newest everything.

Same error on this site, without the infobox.
my server:
FreeBSD 4.10
Apache/1.3.33 (Unix)
PHP/4.3.11 mod_ssl/2.8.22
OpenSSL/0.9.7c
'FrontPage/5.0.2.2635
mod_throttle/3.1.2