Open it photoshop and do a save as and save it as a pdf. I've also had limited success doing this procedure with eCopy to resolve the issue. This issue has been going on since the beginning of wide format printing. These un-flattend pdfs explode into an enormous data stream when you attempt to print them. Its not your fault or the machine you sold.
One other thing to try with these problem pdfs is to print them using the webPrint tool built into the plotter.....I bet they will just work when you do.