Ch 2021 hangs on startup

[Error 403]

Just updated from Ch 2020 which was working fine.    The spalsh screen freezes on 
Initializing (Loading TransmitFullScreen.prm)

Help!

[Error 403]

Update:  Same issue now with both 3.5 and 4.0, after uninstalling/reinstalling both.

[Error 403 · Accepted solution]

The issue in my case was Mediafoundation.dll attempting load codecs from a mapped network drive that was offline.  Bringing the drive back online resolved the issue.