.xls files won't open after upgrading to 1.6.1 from 1.5.1.7

Please check if dokan is installed (windows “apps and features”). The file you have choosen should do the installation.
If it is installed, open cryptomator (make sure it was at least closed once after dokany installation), make sure your vaults are closed, goto “Settings” (right upper corner), go to tab “volume” (second tab) and selekt dokany from the drop down.
Then open your vaults and check.
You can also install WinSFP instead of dokany.