by jason everling.
Within the old config.php for 1.9 did you copy the same $CFG->passwordsaltmain = . If you do not have the same value as in 1.9 then this would cause the login issues.
Also during your upgrade you could have just got the 2.x compatible versions of those plugins like hotpot, journal and such from https://moodle.org/plugins/ and you would not have had to delete them.
JASON