The day this version of Acrobat Reader was released, there were numerous reports of problems saving or printing UnForm generated documents from that product.
After research and testing, we found that Reader 11.0.10 had a new bug related to a certain type of black and white image (specifically, one encoded with CCITT Fax compression). The error and a sample were reported to Adobe, who acknowledged the bug, so we anticipate it will be corrected at a future update by them.
As the error is related to a type of black and white image, you can work around it by changing to a color image for your PDF output. If the current image was generated using our website image conversion utility, you can re-create an image of the same name, specifying a color version, and swap out the color image for the black and white image on disk, at least until Adobe corrects the problem.