Same problem here. One time (I forgot what I did) it complained about permissions but I even tried setting the permissions of the folder to allow everything.
I checked everything mentioned in this topic. I get the same error message (Couldn't create the project directory).
What does ls -ld </folder/to/create/project/in>
and ls -l </folder/to/create/project/in>
say ?
Have you tried to create a project in your home-directory or in "/tmp" ?
Is your disk full ( "df" shows statistics about mounted volumes) ?