Error: Thumb Drive Full

In the office where I work we use a small thumb drive for short term file backup.  If the hard drive crashes and burns, files on the thumb drive will survive.  Later we can save them to a disc for storage.

(The photo is an edited version of a picture from Bing Images.)

One day there was an error message.  The thumb drive was full.  We clicked on "Properties," but there was still quite a bit of free space remaining.

I searched the Internet for a solution to the apparent contradiction that a drive with space available could be full.  One suggestion was that the drive could contain a hidden file that actually used the available space.  Search the help function for "hidden files."  Follow the instructions to show all hidden files on the drive.  This did not help me at all.  

The next option was more severe.  It was suggested that the drive ought be formatted to remove all problems.  First I copied all files on the drive to a new folder on the computer desktop.  But, that also did not help.   Another suggestion was that the drive had become defective and must be replaced.

I brought the problematic thumb drive home and plugged it into a new computer running on Windows 7.  When I tried to save a file to the allegedly full thumb drive, I got the same error message about the drive being full, but with more detail.  The thumb drive uses the FAT 32 file format protocol.  FAT 32 counts files and determines that the drive is full when a certain number of files are stored on the drive, regardless of their size.  The error message suggested making some new folders and grouping similar files within folders.  FAT 32 sees a folder as one file, no matter how many files may be within it.  I removed some files from the thumb drive temporarily and made some folders.  Then I grouped similar files into these folders.  Suddenly our full thumb drive was no longer full and we can now save new files to it.  It does not matter that you may not have Windows 7.  If you are getting an error message that a drive with space on it is full, try grouping some files into folders to restore access to the space still on that drive.