This error might come, if you have skipped any of the Book Keeper Windows version.
However, it can be fixed easily by following simple steps:
Here are the steps:
1. go to C: Drive, go to Program Files or Program Files (x86) then go to Book Keeper folder, then Quickbooks folder, there is one file: SendEmail.exe
2. Delete that file
3. Download Book Keeper from below link and install it.
Download link: bit.ly/bkbwindowsnew
Here's video tutorial for your reference: https://www.youtube.com/watch?v=ca0WTg9Rfn8