The last version of GuideGuide that supported CS5–6 is still available. It is no longer supported and its signing certificate has expired, but does still work if you follow the steps below:

Windows

In the registry go to HKEY_CURRENT_USER/Software/Adobe/CSXS.2 (or CSXS.3 for CS6). Add a new String PlayerDebugMode and set it’s value to 1.

MacOS

Start Terminal.app. You can find this in the Applications folder, or use Spotlight to search for it.

Copy and paste the following command and hit enter. The command below is for CS5. For CS6, change the command to use CSXS.3 instead.

defaults write com.adobe.CSXS.2 PlayerDebugMode 1

Once you’ve done this, restart Photoshop, install GuideGuide, and give it a try. If it still doesn’t work, try restarting your computer.