Why am I having troubles printing from both the Illustrator program and the PDF I save?

I had a large Illustrator file that was made up of AutoCAD linework of an entire university campus.  The file works fine and I can do anything I please. I made a 24" x 36" artboard and scaled an area to fit nicely.  I also deleted a lot of contours and additional linework so the file size was not so large (went from about 40 mb to 6mb). 

However, when I go to "save as" and select my artboard and save as a PDF. I open the PDF, which is 2.5mb in size, and it takes about 1 minute because of all the contours going in one by one. After I let it load, I print to my plotter as I do all the time in Adobe Acrobat X and it will bring up the window that says "Flattening" and gives "1%".  After 10 minutes it reches 2%. After patiently waiting 1 hour, something popped up saying Acrobat failed to complete task and needs to close.  Tried several times and it just wont print! I am Beyond frustrated. I even try rasterizing the PDF by opening it in Ps

Something I note is how my computer is working...that is how it is handling its processes via the task manager.  Both times when I try to print from Illustrator and Acrobat it never makes it because it times out. My 8GB RAM desktop computer reaches max capacity in this process and devotes 6GB RAM specifically to Acrobat or Illustrator as it tries to print.

What is the deal here?  I have "Save As"ed PDF's from Illustrator hundreds of times and sent them to our plotter from Acrobat.  Is there something going on with my Illustrator File?  I idn't think it mattered if linework was outside of the artboard when I save PDF of an artboard.  I have a lot of layers in the .Il file, but most of them are off and it is just linework, no images or effects being done.

Any insight would be greatly appreciated.