When I click on a link in an e-mail (generally to a newspaper article or something like that), I get a box with the following message:

This file does not have a program associated with it for performing this action. Please install a program or, if one is already installed, create an association in the Default Programs control panel.

It seems that the extension associated with such links has gone missing -- can anyone tell me how to find it and then where to put it once it is found so these links will function again?