I have solved this so thought I would share how...
I thought I would create a new Aperture library to see if it was a library issue.
I went to Aperture, created a new library, imported a few images and went back to Safari to upload a photo on the same web page. = Worked perfectly.
I thought I would need to create a new plist / preference file for the old library - but when I switched back to the old library it was working. Hope this simple fix helps someone.
If not - try the steps in http://support.apple.com/kb/HT3805