Usable build volume of a Makerbot Replicator Plus? I've got a class with access to a few Replicator+s. Makerbot's official site gives a build volume of 11.6 x 7.6 x 6.5 ". (LxWxH)

Out of curiosity (I'm not intending to print it), I created a 11.6 x 7.6 x 6.5 inch rectangular prism and placed it in the build plate in the Makerbot software. It didn't like that, so I scaled it back to 11.5 x 7.5 x 6.4 inches to fit inside the build volume. 
It accepted that, and I could click the generate preview button, but then it got stuck 50% of the way through generating the preview and toolpath. I'm guessing that the extruder can't actually reach all of the build volume and so it can't generate a toolpath to create this monstrosity. Does anyone know the actual volume that it can reach and actually utilize?
Exactly what software are you using to slice?  From your description, it appears the gcode was successfully generated, but the software choked when trying to draw teh preview image. That could be due to lack of local RAM or problems with memory leaks in the software.  This happens when the number of layers and the complexity of the layers gets large. 

Try just creating a plain rectangular solid and set a large layer height.  Let us know what happens with that.