Error when opening Word documents

OS: Windows 7 64-bit
Office: 2010 Premium

When double-clicking a .doc/x file in Windows Explorer, or launching it via a different explorer, such as FreeCommander, you may see this error message:

Many, many people have seen this issue. I tried several solution, including deleting the word Data key, as recommended by Microsoft, checking that ‘Run this program as an administrator’ is not checked and renaming normal.dotm, but all failed to fix the error. Finally, here’s what fixed it for me:

  1. Right-click a .doc/x file -> Open With -> Choose program
  2. Select Word 2007 and hit OK.

After doing that, I could open word documents from outside word successfully.