ERROR ITMS-9000: Wrong namespace
 

Hello,
I have an epub file I got this errors when published on apple platorm. How can I fix this errors. I'm using Sigil.

ERROR ITMS-9000: Wrong namespace in /OEBPS/chapter13a.xhtml : null - expecting http://www.w3.org/1999/xhtml

ERROR ITMS-9000: OEBPS/chapter1.xhtml(1): [HTM-049] Html element does not have an xmlns set to 'http://www.w3.org/1999/xhtml'.. This error occurs 22 times. (For more information refer to http://support.apple.com/kb/HT6213)

ERROR ITMS-9000: OEBPS/chapter1.xhtml(1): [RSC-005] Error while parsing file: elements from namespace "" are not allowed. This error occurs 22 times. (For more information refer to http://support.apple.com/kb/HT6213)

Use Sigil's Reformat HTML menu to Mend ALL HTML files to add in the missing xhtml attribute xmlns="http://www.w3.org/1999/xhtml" to each html tags in all of your xhtml files.

Apple uses Epubcheck, so even though others haven't flagged the errors, the errors are indeed there. So it's best to validate your epubs before you upload them to any distributor. There's an Epubcheck plug-in for Sigil, or you can download Epubcheck to your computer.