Acrobat Pro XI Mac won't print a .pdf file, but Apple Preview will print correctly

Question

Hello,
I have Acrobat Pro XI for Mac.  recently I've run into pdf files that will show the document on screen ok, show up on print preview screen ok, but when I send it to a printer I either get:
1.  no printout... the document passes through the printer queue ok, but nothing comes out (no blank paper, nothing).  no data seems to even reach the printer/print server.  no error.  the print job basically vanishes into thin air like the job was never sent
2.  prints out with all the characters of a text substituted with squares (again, no error. just prints squares instead of text)
But when I print the same document using Apple's Preview program on the same machine, the file prints out fine.
I experience this problem with two different Macs, with two different OS versions.  Again both machines will print the .pdf file fine using Apple Preview, but not with Acrobat Pro XI.
I've searched for this problem, but no one seems to have this problem. I've tried just printing one page, etc., and no difference (won't print, or print wrong using Acrobat, but prints fine using Preview)
the files are typically sent via e-mail from a vendor, or a web downloaded form (invoice, forms filled out.  some are secure, some are not).  and these are from multiple sources.
Any ideas what might be the problem, and how to fix this?
system:
Mac Pro (early 2008) and MacBook Pro (mid-2011)
MacOS 10.8.4 and 10.6.8 (multiple computers have this same problem)
Acrobat Pro XI, 11.0.04
printer: HP LaserJet 5MP (yes.. old.. but it works) via HP JetDirect + print server on  LAN

Answer 1

I just found this solution on another board, I tried it  (I removed the same file listed below) and it worked for me.... 
Safari won’t save or print PDFs: how to fix
:: Tuesday, January 29th, 2013 @ 5:29:46 am
:: Tags: Computers
If Safari won’t save or print PDFs (but views them without any problems), you probably have an Adobe PDF plug-in installed. In Safari, go to Help->Installed Plug-ins and do a search for “PDF.” If you have anything with “PDF” in it other than “WebKit built-in PDF,” that is probably the culprit.
On my computer, the problem was “AdobePDFViewerNPAPI.plugin”. To remove it, I quit Safari, did a Spotlight search (Command-Option space) for that file name, and then dragged it to the trash. When I restarted Safari, I could print and save PDFs again. You can also manually find the plugins by going to the system “Library”  folder (the one at the root of your hard disk, not in your user folder) and looking in the “Internet Plug-Ins” folder.
I’m on OS X 10.8.2, running Safari 6.0.2 (8536.26.17).