Since I recently updated Oxide to the latest version I am now getting this server error in console, and MonumentRadiation doesn't load:

Timed out waiting for plugin to be compiled: MonumentRadiation

Any ideas?

Mine is working without any problems, try deleting cs file and reinstalling plugin. plugin hasnt changed in about 10 months

That isn't a plugin issue, and nothing has changed with Oxide in this regard. That message generally indicates that the Compiler is stuck, so it would need to either be killed and allowed to be restarted else the server is restarted.