Tried to download Todoist for Outlook Plug In. Install failed. Error message was to restart and try again, or download VSTO. VSTO is an MS product? I have Windows 8.1 and Outlook 2013.
You downloaded the install file from http://todoist.com/outlook and it gives that error message? If you "Run As Admin" does it make a difference?
The error message asked me to restart the computer, which I did. It then installed successfully.