Help, mendel prusa stops half way every print !?!

I've been printing with my mendel prusa (build with a workshop in the fablab maastricht) for almost a year now.
I was very happy with it till it started to bring errors. this happens now on every print somewhere, I've been unable to print an complete object for weeks now and it is driving me nuts.

The errors what printrun is telling is: serial error last line in not previous line +1.

I've been reading a lot on forums and already changed; USB cable, PC, Laptop and 12V driver. I've completely separated al the cables running from motors and switches , I've downloaded the kliment software new in the sanguinololu chip but nothing worked.

If I check the printrun.exe.log file this is what it says:

Exception in thread Thread-1:
Traceback (most recent call last):
File "threading.pyc", line 532, in __bootstrap_inner
File "threading.pyc", line 484, in run
File "printcore.pyc", line 97, in _listen
File "io.pyc", line 520, in readline
File "serial\serialwin32.pyc", line 212, in read
ValueError: Attempting to use a port that is not open

I'm running on a sanguinololu board with polulu motor drivers.
the 2012 version of printrun.

anybody a clue what will help my printer to function again?
all help appreciated.

Grtz Marc

What baud rate are you running at? I've had this issue in the past running at 250000 baud; changing to 112500 baud fixed this problem for me. Seemed to be a comms issue.

I'm already running on 115200, I've tried lower but still get the error

Are you using linux or windows? If on linux, type the following command into a terminal session to see if you are getting usb port resets due to emi:

grep -i emi /var/log/syslog

For example on my machine I have:

Aug 2 19:07:28 laptop-ubuntu11 kernel: [23960.688148] hub 5-0:1.0: port 2 disabled by hub (EMI?), re-enabling...

I'm using a windows7 laptop, but I've tried it with an apple and had the same errors (at least I think, never checked the log on the apple, because I'm using it not anymore).