I have gotten this error message quite a few times, and I just assumed it was a local problem (most likely caused by print driver problems) - since things are appearing fine on the print preview.
However, experiencing this myself, I started to investigate the issue. It seems to be related with printing png's with transparent background, and it seems like a lot of printers have problems with this(including some very popular HP-printers). It is really nothing you can fix yourself.
I am currently fixing the problem. This involves rebuilding all chord png's with white background instead of transparent background (graphically this does not matter since the page background is white anyway). This actually involves several thousand images, and I have to do it over some time since it will put a lot of extra load on the server.
Expect only some of the images to print while this is being regenerated.
I am sorry for any inconvenience and frustration this error has caused.