Fatal Error - when trying to open project

I downloaded a project from GitHUB in order to work with the repository. When I load the project, it says :

Fatal Error ! Couldn't create assemblies folder! Out of space?

However, I have plenty of space ( over 5 Gb ) on both drives (C&D), and the project is about 1.5 Gb all in all. Could this be because the rest of the team is Unity PRO and I am using only Unity Basic ? or what could cause this ?

I am using Windows 7.