Seems like you are missing the GAB_settings row in the vB datastore table, as all three error have to do with settings. Run the following query and see if you have the relevant row. My guess is that the row is gone, so you'll need to get the row from a database backup:
Code:
# add your vB table prefix to the table name if you used one
SELECT * FROM datastore WHERE title = 'GAB_settings';