ePub errors are a nightmare to fix if you are not technical minded……
I will attempt to help you fix the more basic errors that you are bound to find when you start creating epub files.
1) The first one that you could find:
Filename contains spaces. Consider changing filename such that URI escaping is not necessary
Make sure that you name your HTML file without inserting any spaces!!! IT is that simple, it isn’t the ePUB file that is the problem, it is the HTML base file.
If you get this error recreate the HTML file and don’t try to just rename the file by deleting the spaces in the file name!!! All the images in your HTML document will be pointing to the incorrect directory if you rename the file…. It is way easier to just delete the HTML file and then recreate the HMTL file with the correct name.