If your SD card contains many scans, it can take a while for the scanner to calculate the unused space and determine the number of pictures you can still store. You may want to copy some of these scans to your computer’s hard drive and delete them from the SD card.
Internet Explorer will sometimes produce an “unknown format or damaged file” message when downloading large files. It may help to clear out your temporary internet cache. To do this, go to the Tools menu and click on Internet Options, check Temporary Internet files, then click on Delete. If this does not resolve the problem, consider using a different browser such as Firefox, Opera, or Safari since IE is the only one with this problem.