|
May be silly idea, but ...
Did you uninstall the original Sigil before installing the update (is old version still installed - or did uninstalling remove original and leave newer)
After uninstalling, what happens if you double-click on one of the associated icons (epub) - what does it open with?
If nothing - then re-associate the files to whatever originally opened them.
Then try reinstalling the new sigil (without associating the icons again)
|