138 views but no advice. Ho hum.
I did manage to pin down 18 September as the last successful use of Sigil. What happened to it between then and the 24th is still a mystery. Looking at installed software these are the only things that might be candidates:
19/9 Android SDK Tools [hmm...seems an unlikely cause]
20/9 MSXML 4.0 SP3 Parser [Windows Update I think]
22/9 MSXML 4.0 SP3 Parser (KB2721691) [Windows Update again]
Is using 0.5.905 a viable idea?