What does failure to load its core DDL mean?

As of today, I am unable to open pdf's. The following message comes up:

"Cannot open in protected mode due to incompatability with your system config. Would you like to open Adobe Reader with protected mode disabled?" When I click yes, the following ststement comes up: "Acrobat failed to load its core DDL".

I downloaded version 11.0.02 and get the same messages.

I am using Windows 7.