by Ken Task.
Change max all the time (up/down) and have never had such a change (done correctly) whack a Moodle, or a Joomla, or a WordPress site.
Now this is far fetched, but am wondering ... because you said you couldn't login ... and that's tied to sessions ... IF ... notice that's in CAPS ... the setting for the max size may have been mistakenly set to KB and not MB.
post_max_size = 200 is not same as post_max_size = 200M
'spirit of sharing', Ken