What version of Adobe Reader X are you using? I know I have had all sorts of issues with 10.0.1 and updating to 10.1.0 seems to be a much more stable option.
I also saw this problem you are having and hitting F5 to refresh the page seemed to magically cause the document to display (not a resolution but something to try)
Thank you for this.
One you said this I checked and it was running IE 64bit.
For some reason IE*64 was the default browser (which shouldn't happen). Since IE*32 wouldn't allow me to set it as default (greyed out) I installed Chrome, set it as default browser then fired IE*32 back up, set it as default and vioila it's fixed.
I'm embarrased I didn't think of that first....