The command C:\Program Files\Epic Games\UE_4.26\Engine\Build\BatchFiles\Build.bat TycoonSourceEditor Win64 Development -Project=C:\Users\Greg\Perforce\myworkspace\TycoonSource.uproject -WaitMutex -FromMsBuild exited with code 6.
The error you’re copy-pasting is a follow-on error. You have to scroll back up in the log and figure out what the actual root error is.
Chances are, some files that are necessary, didn’t get checked into source control. Or, slightly less likely, some file that needs to be generated, was checked in as read-only, and can’t get re-generated.