[2021] "An Error Has Occured" when trying to start game/launcher

Try shutting down anything that might be interfering with Warframe's launch, (like Razer Synapse, Discord, various screen-recording programs). You could also try disabling the Steam overlay by right-clicking "Warframe" in the game list, clicking Properties, and it's a checkbox on the first page.  If none of that helps your best bet is to contact Support, and send in your Launcher.log file  (found under Start, Run, "%LocalAppData%\Warframe\" )