MakerBot Replicator 2 fan duct hitting print

[ammeryw]

Hello, I am using a MakerBot Replicator 2. I am not exactly sure why this started happening, but on my last few prints once they start to get a bit of height, the bottom of the fan duct next to the extruder nozzle will ram into a corner of my print and knock the whole gantry back, ruining my entire print. I'm not that knowledgeable in this stuff, and don't really know what I did wrong. Here's a pic of the fan duct and nozzle.
Thank you in advance for your advice!
http://imgur.com/jzspKYW

[Chemvaldes]

I was going to say make sure that the shroud is "clicked" in place but from the picture you posted it looks just fine. I have had a lose corner of a print "unclick" my shroud before but never had it hit during a normal print.