Chris -
The latch may be closed: pull the handle & see if it opens. If so, that's the start of your problem. Then try to latch the door. If it won't latch closed completely you may have to adjust the strike as MBB suggests.
If the latch is open with the door open, make sure it's closing completely by pushing in on the "trigger" with the door open. If it doesn't snap shut you probably have a worn or defective latch. Could even be gummed up.
In any case, if the strike isn't aligned correctly it won't work right. Check your door gaps 1st, though.
Prolly tweaked the body by dropping a wheel in a hole & jacked the door alignment.