Unrecoverable build error - whilst trying to build setup on VS2015

My build fails every time when I try and build my setup project. The error in the output window is just:

ERROR: Unrecoverable build error

What I have tried already

• Restarting my computer and Visual Studio
• Registering ole32.dll
• Clean and rebuild all
• Deleting bin and obj folders
• Removing temporary files with VS in the name in \AppData\LocalTemp
• Running Visual Studio as an administrator
• Pausing the real time protection on my antivirus
• Deleting the temporary file that the setup build leaves in there.
• Running the process monitor during the build.
• Checking if my project contains duplicate folder names (it does not).

Note: Similar question but not the same as it is for a much earlier version of Visual Studio:

• "Unrecoverable build error" on any MSI Setup project
• “Could not create the file”, “Access is denied” and “Unrecoverable build error” in building setup project in VS 2008

The problem was solved by registering mergemod.dll.

On my computer it is located at: C:\Program Files (x86)\Common Files\Microsoft Shared\MSI Tools

You need to run regsvr32 with administrative privileges to get it to work.