Unfortunately I have not made any progress.
I have reinstalled apache following the Perfect Server script but there is no change.
So all clients/users websites run ok but ispconfig, squirrelmail and phpMyAdmin don't.
trying to connect to phpMyAdmin, Squirrelmail and Webalizer give an "Unable to connect" message
The apache error log shows "...client denied by server configuration..."
ISPConfig3 gives "...there was an error in a CGI script." message
the apache error log shows "...No user or group set - set suPHP_UserGroup..."
The other error is that I cannot upload mail. It is arriving ok but uploading to a mail client fails