Logging in Richtextbox inside thread

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C#

WPF

Hi all

Okay, this must be some kind of monkeytest, but I just dont get it.

I have WPF UI where I have richtextbox "myLog". Also I get data now and then which could need logging. When my event call my Log method I receive error:

"The calling thread cannot access this object because a different thread owns it"

And here is simplified idea of my logmethod:

//LogMsgType msgtype: Error/Incoming/Normal/Outgoing,Warning , string msg: message 
private void Log(LogMsgType msgtype, string msg)
        {
        myLog.AppendText(msg); //here error occurs 
        }

i really appreciate your advices :)