Error 17 Unknown build error, 'An item with the same key has already been added.'

I recently got this error after doing a code merge. No source file, no line number, just the project name and nothing else to point me in the proper direction to rectify my issue.

After much searching I found the answer to my problem in this post.

The post states this can occur if there are duplicate lines within a <ItemGroup> node in a csproj file.

I did a compare on my project file and found this.

I removed the duplicate line and everything was right with the world again.