Win32 error 3 (see complete list here) corresponds to "The system cannot find the path specified."
You might be exceeding the maximum path length supported by Windows (260 characters by default). Instead of the extremely long, complex and confusing directory names that you are using, I strongly suggest something more practical such as "C:/Astro/M101" for example. As for file names, how about "dark01", "dark02"... etc. Well, it can be slightly more elaborate, but you get the idea.