Snapshop Pro not transferring 500MB backup to Dropbox

Hi Folks

A full database & files snapshot is not saving the snapshot file to Dropbox.

This is a multisite install, and the subdomain sites are working fine and saving to dropbox.

The admin area shows the message: Destination: Fail

There is plenty of room in my Dropbox. The only difference is that the backup file is 500MB.

Creating a database only snapshot of this site works fine and stores to dropbox.

Many thanks.