“When trying to run the project, I receive the following error: System.AggregateException: One or more errors occurred.”
Solution
The problem is that UiPath.Service.Host process (the robot) was not restarted at all after the upgrade.
This can be done by killing the process in task scheduler, restarting the robot tray or logging out/logging in to your windows account.
Ref:- V2018.3 UiPath Community Edition - Troubleshooting Guide - Help - UiPath Community Forum
Hope this helps 