A thrid computer just came into our shop with a similar problem involving Adobe Reader.

We started looking at what was the same between all three computers. Any computer that comes into our shop with a current and active antivirus subscription, gets Panda's Cloud free antivirus product installed on it. They have a new component called Data Shied. That is the problem. Disabling this feature fixes the issue. We will be uninstalling Panda and finding another free solution for our customers.