DavkaWriter and Windows’ Hebrew language support try to use the same reserved keystroke – Alt+Shift. If you are using DavkaWriter on a system that has Windows’ Hebrew language support installed (the EN/HE language selector) and you use Alt-Shift to switch languages, Windows will switch to Hebrew mode, which is not compatible with DavkaWriter.
In order to type Hebrew in DavkaWriter, Windows must be left in English mode (the EN option). You can then switch languages in DavkaWriter using Alt+/ or Alt-. instead of Alt+Shift.