Error 21 or DW021 installing Photoshop

When you try to install Photoshop CC 2015 on Windows, you get Error 21 or ERROR: DW021 in install logs.

Solution

1. Run the Creative Cloud Desktop uninstaller

2. Rename the following folder:

C:\Program Files (x86)\Common Files\Adobe\OOBE\PDApp

to

C:\Program Files (x86)\Common Files\Adobe\OOBE\PDApp_old

3. Install the latest version of the Adobe Creative Cloud desktop app.