2020.2 Upgrade Error - There was an error running this app: Method Not Allowed

Question

Upgraded server to 2020.2 and am now unable to run any workflows.  All workflows (and apps) display the error

"There was an error running this app: Method Not Allowed".

Also unable to view recent recent results.  When clicking on an old "Workflow Results" the gallery page becomes stuck on the "loading" screen.

naleti · Answer

Last night we upgraded from 2020.1 to 2020.4 and had similar issue. We cleared browser history and things worked fine after that. Thank you

pjarrard · Answer

Never mind - solved my own problem.

Forgot to clear my local browser cache after upgrading (a time-honored trick to solving all sorts of upgrade glitches).