Please see my comment to the question. A code sample won't help you; especially you did not explain what you are trying to do. If something is not supported on some platform, it is just not supported; you only can 1) change this platform; 2) do something different on that platform.
What really could help you is looking critically at your own questions. You need to explain your goals, formulate what you want to do precisely, provide precise exception information, and so on.
You general problem is: you are probably trying to use obsolete (non-UTF) encoding on a Unicode-based platform, which also is not supported on the platform you are using. You should also understand that there is no such thing as miracle. :-)
Please see exception information on the MSDN help page on the method:
http://msdn.microsoft.com/en-us/library/wzsz3bk3%28v=vs.110%29.aspx[
^].
See also:
http://msdn.microsoft.com/en-us/library/system.notsupportedexception%28v=vs.110%29.aspx[
^].
—SA