Try then the Microsoft Troubleshooter which usually fixes installation and uninstall problems.
See the following eM Client thread for info.
https://forum.emclient.com/t/cant-upgrade-em-client-8-to-9-or-even-uninstal-em-client-8/81275
“Microsoft webpage info”
How do I Fix problems that block programs from being installed or removed.
Note:- Failing that as per the thread link at the top, if still the same issue you will need to contact Microsoft Technical support.