There was a change in the spec. Page-masters (like simple-page-master) have a master-name. Things that refer to page-masters (like page-sequence) now have a master-reference instead of a master-name. You will have to change your fo:s and whatever is generating them to conform.
[ERROR]: 'master-reference' for 'fo:page-sequence' matches no 'simple-page-master' or 'page-sequence-master'
<fo:simple-page-master master-name="main" margin-right="1cm" margin-left="1cm" margin-bottom="1.5cm" margin-top="1cm" page-width="21cm" page-height="29.7cm">
</fo:layout-master-set> <fo:page-sequence master-name="main">