puzzling

Installed aegir a couple of days ago - and I really, really like what it offers!

But I have a really wierd problem with the "File system" settings...
It says:

• The directory sites/[testsite]/files is not writable
• The directory sites/[testsite]/files/tmp is not writable

And I have "even" tried chmod 777 on the folders!!!

The main hostmaster aegir site works and validates that the files folder is writeable - and if I chmod that to 550 it complains... why can't the hosted sites connect to their files folder??? What am I missing and how can I solve it?