Usually the error message tells you what the problem is, so you can easily fix it with your ebook or picture editor program (e.g. Sigil or IrfanView). Once you have fixed the issue, you have to upload the corrected file. Please press the Fix... and the All issues fixed buttons, so our colleagues know to review the book again.
We review your book again, and if there are any issues left, we will contact you.
Otherwise your book will be published in the stores of your choice.