My Personal Storage is not Filled up yet, Nevertheless I Cannot Create New Files

The quota on personal storage is limited. This means that if you create more files than possible you will get a error message like "drive full", even if the amount of data is still below the GB limit.

You can check the number of files and the usage of the capacity on a web interface. To make space for new files you can delete some files or pack files in an archive like ZIP or RAR.