"An error was thrown." is received if the m key in the combination cntrl+shift+m (central math block) is pressed too fast - if I delay the m click of the combination no error, if I press it too fast, error is received. I use the latest .deb version.
See image:

Appears to be an issue for both English and Hebrew.
This is a an exciting project! Keep up the great work.
Cheers,
Tom