This is most likely either because you have the Internet Explorer plugin disabled. To enable the plugin, you will need to do the following:
Step 1: In Internet Explorer, go to “Manage add-ons” (You will need to have attempted opening a document first otherwise the plugin will not have been loaded into IE)
Step 2: Locate the “MindViewOpen Class” plugin and make sure that the plugin is enabled.
You must have MindView 4 or newer installed for the Internet Explorer Plugin to be installed.