Your display is set to 120 DPI. The Developer only supports 96 DPI.
From UPK wiki
The following messages are displayed (in a dialog box) when you try to start UPK (possibly the first time you start it after installing on your machine):
Your display is set to 120 DPI. The Developer only supports 96 DPI. Change your display settings and start the developer again.
- Go to Windows > Control Panel > Display.
- Under Make it easier to read what is on your screen, select Smaller - 100%.
- Click Apply.
- Restart your PC.