Hi Olivier,
OpenToonz remember the tool state in personal settings and reproduce it on the next launch.
Installing OT again will NOT remove the personal settings.
( Even if you actives "Overwrite all setting files in the Stuff folder except user's personal settings" checkbox in the Windows version installer, it will literally keep the personal settings unchanged. )
This crash occurs if you finished OT with "Lines" mode being selected in Fill Tool. On next launch, OT tries to reproduce the "Lines" mode and crashes when initializing Tool Options interface for Toonz Vector level, because there is an option which is available only in Toonz Raster level.
It was my fault as I could not detect the bug when I added such option. So sorry for the trouble!