I am working through the creation of my first epub file and am at the stage of testing it using http://validator.idpf.org/
One error I keep getting is this:
Extra field length for first filename must be 0, but was [BIG NUMBER]!
From what I've read, this is because one of the two folders in the .zip archive is getting read before the mimetype file. So... I'm trying to use 7-Zip via the command line, because using 7-Zip that way (probably command 'x') looks likely to be able to preserve the order in which the files & folders were added to the zip archive, i.e. keep mimetype at the top.
However - a whole new problem - I can't get the command prompt to do anything, even after having configured it to open directly in the folder of my choice.
I'm feeling stuck here. There must be a way of getting the mimetype file to get read first - and I would really appreciate it if anyone who's had the same problem could let me know.