Your form runs on a different thread so you can't call members just like that. If it's a normal winforms application you can use the Invoke method.

For example:
Code: 
// some code running in a new thread
// change the text of a label on a form:
this.Invoke(() => this.lblTest.Text = "my string");
http://msdn.microsoft.com/en-us/library/zyzhdc6b.aspx
Hyperz Reviewed by Hyperz on . [C#] Thread Safe in - How to? heya guys Im working on a C# Application and im having some issues with the ThreadSafe thingimabob. When i try execute the a command i get the Thread not safe. heres my Code! using System; Rating: 5