Insufficient data for image (Adobe)

This is getting frustrating. We have staff that view, print, and email PDFs, some of which are 5 – 6 years old. Within the last two weeks, we are seeing the error: Insufficient Data for Image, when using Reader 7 to open the file. We have found a workaround; use 8.1 reader and this allows the file to be opened no problem. To print it, we have to change the advance setting to print as image and use the PCL driver for whichever printer we are sending to.

Can anyone shed some light on why this is happening all of a sudden.