Follow the steps below to reinstall Paint Tool SAI:
1. Open SAI installed folder.
2. Right click on document named help.
Answer for this issue:
1. Lunch PaintTool SAI installer for full installation.
2. Enter “C:\PaintToolSAI\” to [Installation Folder:] input box.
3. Press [Install] button.
4. Reinstall your product permit authentication again only if you have license for SAI.