Hello Cristine,
the problem has to do with the character "#" appearing in the file name of some of your images, since it has a special meaning in HTML code. You should generally avoid to use any special characters in your assets names.
PubCoder already replaces some special characters, we will add "#" to the list. In the meantime, to fix the issue, please rename those assets by removing the "#" character:

• Click "Assets" in the left panel of your project window
• Check that the "kind" of assets below the Assets tab says "Kind: Images" or click on it to switch
• Click "Search Assets" in the bottom left of your project window
• Type "#", the list will filter filenames containing a "#"
• For each of those files, right-click and choose "Rename"
• Remove the "#" and confirm by clicking hit enter: the entry will disappear (since it does not contain the "#" character anymore and we are filtering for it)
• After doing this for each file in the list, save your work and build your EPUB again. It should not contain errors anymore.

Best Regards,
Angelo