well. first i would say
#1 check your blade mounting bolts to make sure the blade is mounted properly. If that is ok then.....
#2 check your spindle for looseness. If that is ok then......
#3 check the bolts that hold the shroud in place by the wheels, make sure they are adjusted properly and tight. If that is ok then...
#4 BIG HAMMER move the blade and give that shroud a big whack with a 3lb sledge hammer until the blade clears.
(Always take the spark plug wire off the spark plug when working on the underside of the mower)