Shortly following this exception, I tried to create the directory myself

  C:\...> mkdir slut-0.9\aux
  The directory name is invalid.

Curiously, I searched the internet for why a directory named 'aux' 
cannot be created anywhere on the Windows filesystem. The reason - this 
is a 'special' name: http://www.blindedbytech.com/2006/11/16/forbidden-
file-and-folder-names-on-windows/

However, does this mean one can never create a directory named by these 
special names? Apparently .. that is what I think is the case. I cannot 
even create a folder named 'aux' using Windows explorer!