Site 5 Install error

All,

Finally got Radiant .6 to work on Site 5 yesterday - but when I now go
to a
page to edit I get the following error:

Application error (Apache)

Change this error message for exceptions thrown outside of an action
(like
in Dispatcher setups or broken Ruby code) in public/500.html
This happened yesterday too, I get it installed. It works fine, then the
next day I get the error.

I need to install Radiant for around five sites in the near future and
this
is driving me nuts (!). Can someone help me offline so I can overcome
this,
I can’t see why .5.2 was so straightforward yet this upgrade is causing
me
nightmares!

Can any1 help?