Errori formato epub, mi serve aiuto

Buongiorno,

ho creato un formato epub del mio libro che dei siti di valutazione di file epub ritengono corretto, ma non mi viene accettato da lulu.com che mi segnala i seguenti errori:

ERROR: Unable to locate a valid creator. A creator with the author role (role=aut) and the file-as attribute is required in OEBPS/content.opf
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0004.xhtml
ERROR: Unable to locate element with id 'heading_id_1' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0006.xhtml
ERROR: Unable to locate element with id 'heading_id_2' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0008.xhtml
ERROR: Unable to locate element with id 'heading_id_3' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0010.xhtml
ERROR: Unable to locate element with id 'heading_id_4' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0012.xhtml
ERROR: Unable to locate element with id 'heading_id_5' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0014.xhtml
ERROR: Unable to locate element with id 'heading_id_6' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0016.xhtml
ERROR: Unable to locate element with id 'heading_id_7' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0018.xhtml
ERROR: Unable to locate element with id 'heading_id_8' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0020.xhtml
ERROR: Unable to locate element with id 'heading_id_9' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0022.xhtml
ERROR: Unable to locate element with id 'heading_id_10' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0024.xhtml
ERROR: Unable to locate element with id 'heading_id_11' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0026.xhtml
ERROR: Unable to locate element with id 'heading_id_12' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0028.xhtml
ERROR: Unable to locate element with id 'heading_id_13' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0030.xhtml
ERROR: Unable to locate element with id 'heading_id_14' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0032.xhtml
ERROR: Unable to locate element with id 'heading_id_15' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0034.xhtml
ERROR: Unable to locate element with id 'heading_id_16' in OEBPS/toc.ncx
ERROR: IOException: Unresolved external XML entity: 'http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd' in OEBPS/text/content0036.xhtml
ERROR: Unable to locate element with id 'heading_id_17' in OEBPS/toc.ncx

 

Qualcuno potrebbe aiutarmi per cortesia? 

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