I had the same issue. For the record. Here's a quick review of how I got MusicBee to start.
I picked a new skin (don't remember which) and MusicBee crashed and wouldn't restart.
Following the suggestions given in this thread I navigated to:
C:\Program Files (x86)\MusicBee
and renamed the Skins folder to xSkins as below.
C:\Program Files (x86)\MusicBee\xSkins
After that MusicBee opened without any hiccups, with a default skin.
Then I renamed xSkins back to Skins and picked a new skin.
MusicBee closed and reopened to the new skin.
---
2/24/2020 8:01:02 AM - 10.0.17763.0 - 3.2.6827.32939 -
System.TypeInitializationException: The type initializer for
'#=zWgVSKukqeXygRQzGXqeUxNg='
threw an exception. --->
System.NullReferenceException: Object reference not set to an instance of an object.
at #=zWgVSKukqeXygRQzGXqeUxNg=..cctor()
--- End of inner exception stack trace ---
at #=zWgVSKukqeXygRQzGXqeUxNg=..ctor(Boolean #=zV9eAh3T8Ivy6eWUzPA==, Boolean #=zfKHrQhLCbj2d)
at #=zxi2ztvXlrgvl0YoLwsbUcbLajWOM..ctor()
at #=zl3G$ts$_9zIRoQdlmns30$2c9Koz.Main(String[] args)