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()'
System.MissingMethodException: Method not found:
'System.String System.String.Format(System.IFormatProvider, System.String, System.Object)'.
To resolve, I simply needed to replace it with TracingService.Trace(message,null);
This issue is caused by compiling the Plugin using the 4.6.2 version of the .NET framework - so by compiling against 4.5.2 the exception no longer occurs.
Hope this helps!