When trying to install eTakeoff, "Error 1609" indicates that you need to add "Authenticated Users" as a group to your computer before installing the software. This most typically happens when your computer in configured for another language other than English.
Follow the procedures below.
1. Go into your Control Panel
2. Click on Administrative Tools
3. Click on Computer Management / Local Users & Groups / Groups
4. Right Click and select New Group
5. Type in "Authenticated Users"
6. Click on Add User
7. Install eTakeoff