I recently found an issue with Dynamics 365 Version 9 where a call to ITracingService.Trace(message) from inside a plugin caused the following exception:

 

System.MissingMethodException: Method not found: '!!0[] System.Array.Empty()'

 

Or

 

System.MissingMethodException: Method not found:
'System.String System.String.Format(System.IFormatProvider, System.String, System.Object)'.

 

 

I simply needed to replace it with TracingService.Trace(message,null);

UPDATE: This issue is caused by compiling the Plugin using the 4.6.2 version of the .NET framework!

Hope this helps!