Problem: 

When starting Visual Studio 2015, the following message is shown

“Setup error – repair/modify operation did not finish successfully.”

Resolution:

This message is shown when a repair was previously performed on the Visual Studio 2015 software but it was not able to successfully complete.

To resolve this issue amend the following registry key:

HKEY_LOCAL_MACHINE\\SOFTWARE\\Wow6432Node\\Microsoft\\VisualStudio\\14.0\\Setup\\VS\\professional

 IsInstallInProgress key should be set to 0