Hey! I've tweaked the error handling and added some logging so maybe we can figure out exactly where the problem is.
Can you first delete all traces of the plugin:
From the MusicBee\Plugins directory:
Delete mb_GoogleMusicSync and Newtonsoft.Json.dll
and any other files with the same name (but different file extensions) - if there's anything that ends in .pdb, .dll, .xml or .config with either of those names, delete that.
From the C:\Users\<yourUserName>\AppData\Roaming\MusicBee directory:
Delete gMusicPlaylistSync.Settings.xml and gmusicStream.Settings.xml if either exist
Then download version 1.6 from here:
https://github.com/leoedin/MBGmusicSync/blob/master/Plugin/mb_GoogleMusicSync_v1.6wLogging.zip?raw=trueExtract the 2 DLL files there into your MusicBee\Plugins directory
If MusicBee still fails to launch, the version I've linked above saves a log with some of the steps it's taking to C:\Users\<yourUserName>\AppData\Roaming\MusicBee\gMusicPlaylistSync.log.txt - post the contents of that (if it exists). If it doesn't exist, let me know.
I've changed the plugin to add a menu item under the Tools menu - look there to launch it.
Let me know how that goes!
Note: This version logs quite a few things to file, and the log will keep growing. If it works, check back for an updated non-logging version.