unable to upload files after moving WordPress install

I have recently moved a WordPress install from a folder to the root of the server and after a bit of huffing and puffing managed to get all the links and everything working correctly.
However, when I now go to upload an image or document file I get the following:
“document-name.pdf” has failed to upload due to an error
The uploaded file could not be moved to /var/www/html/main/wp-content/uploads/2012/12.
With some detective work on the forums I have managed to get this to work, but only by applying 775 permissions to uploaded folder. There are strong recommendations not to do this from other threads I read.
The files are going to the right folder (when working) and changing the permission back to 755 doesn’t allow uploading to continue (one comment mentioned in another thread).
As this worked on the WordPress install before moving, I can only think that this is a configuration issue in either php, Apache or WordPress, but I can’t find any reference to this in the forums.
Incidentally, I thought that uploading a file would go into this months folder, but it seems to go into the folder relating to the date the page was created.
Any help will be gratefully received.
Mick