Its hard to tell from the distance what the cause for that behaviour could be. As other people can view the files w/o problem it seems that the file is OK (Mathe Nexus files are created with rather old versions of Mathcad, but this usually is no problem).
Which OS is MC installed on. There are reports of 3D-plots not working under Win7 or Win8 and one of the workarounds is to decrease colordepth (from 32bit to 16bit). Not sure if this would help in your case as I am not aware having read about a 2D display problem before.
When you installed MC, was there a situation when MC wrote that it would need certain files, you clicked continue and MC seemed to install w/o problems nevertheless?
Do you encounter that problem only with precreated files from the same source only or does it happen with plots you create yourself, too?
Is there a pattern, e.g. is it always the first plot in file which does not show up correctly (as in the file you posted)?
Does dragging the plot region around the page change anything?
Do you get the format-menu when you doubleclick the plot region?
Does it help if you save the file immmedeatly after opening in MC15 format and then open that file?
Sorry, I'm just poking around without having a distinct clue.
You may consider calling PTC support - maybe they know about that effect.
