thread problem in textbox control access!

Question

Hye everybody!

I've got a problem with a textbox access. I'm using VS2008, WPF, c#.
I've got two projects in a solution. In one project i update an xml doc. In the other project, in wich my textbox is declared, i have declared a FileSystemWatcher who detect when my xml doc change. When it changes i whant to put a text in my textbox. Unfortunatly it raise a InvalidOperationExeption and write: "The calling thread cannot access this object because a different thread owns it.". I don't know how to solve this problem. Is anyone can help?