I spent a long time deleting chapters etc. and ran into problems after validating. I tried to open saved file with Calibre and could read it with Calibre viewer but when I sent it to the ebook it again would not open.
Frustration was setting in so I tried another method. I converted the file to mobi, deleted the epub file and converted the mobi file back to epub with the "split files larger than 260 kb" (I had tried converting from epub to epub but got nowhere).
To make a long story (very long
) short I transferred the new epub file to the Bebook and it opened.
Many thanks for your advice and I must spend some time learning about Sigil for the next problem that arises