Hi Renan,
Since Shared Bundles 10.3 XMLTools Fix 3 was already installed so probably it doesn't allow you to select the same Fix Level for Install.
Can try either of the below and check if it helps
- As per the Solution link you have posted
- Open/Run Command Prompt App as Administrator
- Change Directory to the folder where the file UpdateManagerGUI.bat exists
- Run the command UpdateManagerGUI.bat -overInstall true
- The Update Manger UI must open and now you shall be able to select the same Fix to Install
- First Uninstall this Fix and then Install it back