"General error occurred return value is 1603" or "1603 - Fatal error during installation" warning given when trying to install TOAD for DB2.
The user does not have proper admin authority on his PC to run the installation.
.NET Framework system requirement is not met.
User needs full admin privileges for instalaltion. Verify privileges with the system administrator. Verify UAC setting.
Ensure the .Net Framework versions are installed properly. Check the specific version's system requirements for .NET in the release notes here.