Originally Posted by ldolse
You can try opening in MS Word - it sometimes can repair corrupted rtf files, and then save/export as filtered html from there and import the html back to Calibre.
in my experience that repair rarely works, if ever. if a convert TO .rtf fails then its better to convert those specific files to txt instead, & accept some loss of formatting, then go txt to rtf or whatever via word.
I have never seen a convert FROM (good) .rtf fail