Good oh!
Disclaimer: Only do this if you understand exactly what you are doing.If you did want to tidy up and avoid any problems next time ....
- Delete the TR5 and AT4 dll files from "C:\Program Files\Steinberg\Vstplugins\",
- Uninstall TR5 and AT4,
- Install TR5 and AT4, making sure that you select the "C:\Program Files\Steinberg\Vstplugins\" folder for the VST plug-ins.
It might even be better to create a new folder "C:\Program Files\Steinberg\Vstplugins\IK Multimedia" and select that as the destination.
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Background info
The "C:\Program Files\Steinberg\Vstplugins" folder is the one suggested by Steinberg (the originators of the VST plug-in format). Initially other developers used that folder too; but these days, more and more are moving away from it. And most installers these days let you select the folder for your VST plug-ins. Just remember to check each stage of the installation; do not just click [Next] or [OK] without consideration.