I've had similar error in production. We had linux server with C++ program doing many things, and in the process it created temporary files for a barcode printer. The files were named uniquely, the server had lots of free space, we left them there to allow easier debugging if sth wrong happened (it happened a few times each year - we created the labels to print by glueing escape codes and sometimes there were labels that didn't worked for one reason or another), and only cleaned the old files when there was not much space left.

At some point there was a bug when sometimes users got "wrong permissions or no space left" errors (sorry don't remember the exact error and IIRC our app just tried to save a file and failed with unspecific error if it couldn't write the new temporary file, so we haven't had the exact system error).

What was weird is - there was still lots of space on that disk, permissions were OK, and I've tried creating new files there, both from our app and by hand and it worked.

It turned out after a few days of frantic debugging, that when there's too many files with similar names in one directory - creating a new file can fail because of hash conflict, depending on the filename only. So,

    ls A1234.txt S1234.txt # no results
    touch S12345.txt   # fails
    touch S1234.txt   # works

:) It was one of the biggest WTF moments I had while programming.