AfterUserRegistration is only fired for frontend CB registrations. If you're creating users in backend it won't do anything. You'll need both AfterUserRegistration and AfterNewUser. If you're getting errors then enable debug mode and maximum error reporting in Joomla global configuration to expose the errors. If you have both queries in the same action and you didn't separate them properly then it'll error as the query needs to be terminated with ; and linebreak.
Code:
INSERT INTO `j25_virtuemart_vmusers` ( `virtuemart_user_id` ) VALUES ( '[user_id]' );
INSERT INTO `j25_virtuemart_userinfos` ( `virtuemart_user_id`, `last_name`, `first_name`, `phone_1`, `address_1`, `address_2`, `city`, `state`, `virtuemart_country_id`, `zip` ) VALUES ( '[user_id]', '[lastname]', '[firstname]', '[phone]', '[location]', '[address]', '[city]', '[state]', '[cb_select_country]', '[zipcode]' );