If you are using the 2.48.05 version of Git Extensions and have changed the git command to the most recent 64 bit version of Git for Windows from the Internet, the main menu item GitK under Tools doesn't work anymore. You can fix it as follows.
Now you can run GitK from the menu item Tools/GitK.
- Go to the folder "C:\Program Files\Git\cmd"
- Create a text file named "gitk.cmd"
- Copy and paste the following code into it.
@cd %~dp0 @start "" gitk.exe %*