Why do I receive Error Code 115 during license activation?

Symptom

While trying to activate Gaaiho with a license code, a message shows Error Code 115 and activation fails.

Explanation

The License Code or Serial Number entered did not match the currently installed Gaaiho PDF software.

Solution

You can either (1) download and install the correct version of Gaaiho PDF; (2) upgrade to the latest version of Gaaiho PDF.

(1) Download and install the correct version of Gaaiho PDF:

Remove your current Gaaiho PDF software;
download the correct version that matches your license (click here to download older versions);
install (for Gaaiho PDF 3 or earlier versions, please download the software that matches your Windows OS: How to check which Windows operating system am I running?)
activate (How do I activate Gaaiho PDF 5 online/offline?).

(2) Upgrade to the latest version: