It's not good not to give use full type name, such as full name of
UserControl, at least once — please see my comment to the question.
You cannot call anything related to UI from non-UI thread. Instead, you need to use the method
Invoke or
BeginInvoke of
System.Windows.Threading.Dispatcher (for both Forms or WPF) or
System.Windows.Forms.Control (Forms only).
You will find detailed explanation of how it works and code samples in my past answers:
Control.Invoke() vs. Control.BeginInvoke(),
Problem with Treeview Scanner And MD5.
See also more references on threading:
How to get a keydown event to operate on a different thread in vb.net,
Control events not firing after enable disable + multithreading.
—SA
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