Check the NS Plus version. Should be at least 4.10.04 to handle the later Acrobat versions. One is probably not at the later version.
There may be a later version than 4.10.04, but Xerox said that this was going to be it, no more NS Plus updates. I haven't personally seen anything later.
This was a very common NS Plus problem with earlier software versions when Acrobat 5 came out. A workaround prior to the Xerox fix was to maintain a copy of Acrobat 4 on the submitting workstation, open the Acrobat file in 4, and print it from there. This worked well enough for 5, but when 6 and 7 came out, the files created with 6 or 7 often would not open in Acrobat 4. You can load Acrobat 4 along with the later Acrobat versions. You have to launch 4, then open the pdf within 4. Double clicking on the pdf won't work.
NS Plus is prone to software corruption as well. If the version is up to date, then a software re-load will probably fix the issue. This is a software rip, no PDCIM or other interface card. You could check transceiver at the Doc I guess.
Untimate solution of course is to convert the machine to a 6135 with an up to date controller.
