I just cleared out silverstripe-cache folder, made sure it was chmod 777, and tried the site again.
It has written two files in there - manifest-index and manifest-main
and then stopped with the fatal debug not found error in the log
A bit weird that it does this on a fresh install !
Seems I spoke too soon - and didn't read too well: The error message states that you have access to your root folder and to /tmp/ as well. So my interpretation of your error message was off I guess- sorry for that :-(
But it seems that there definitely are issues with open_basedir and plesk. I found this, and there is more (no, there is nothing missing from the url):
It was indeed the open_basedir settings changed in plesk- it had suddenly acquired a final slash.
But when SS calculates it's BASE_PATH it doesn't have the last slash (on 2.4.5) and so fails the "in path" test and thus fails to build the manifest properly and stops with fatal errors.
Just had to make a tweak to Core.php to add a final slash and suddenly all the errors went away and I was back up!
Thanks guys for the ideas and moral support - invaluable !!!!