Having trouble with background threads and exceptions

Hey guys,

Here is the scenario:

I have the main form open and a background thread is running. The
background thread sometimes needs access to the main forms graphics object
and gets it by calling Graphics g = CreateGraphics( ).

Now, I close my main form while the background thread is running and when
the background thread gets to the CreateGraphics( ) line, it throws an
exception (since the main form has been disposed).

I couldn't think of any way to prevent that exception from occuring. Since I
need the forms graphics object to use in that background thread, and checking
if(!this.IsDisp osed) isn't guaranteed to always work, I thought I can at
least log the exception. However, that doesn't seem to work either.

The background thread method is enclosed in a try..catch block and in the
catch block I have:

using (StreamWriter sw = new StreamWriter(@" C:\Errors\Log.t xt"))
{
sw.WriteLine(Da teTime.Now + " [ERROR] " + ex_.Message);
}

When I'm debugging, if I close my main form and, if the exception is thrown,
which is not always, break on the WriteLine I can see the error message fine.
However, after the app closes, the file "Log.txt" is created but is empty.

Does any one have any ideas as to why? I also tried displaying a MessageBox
with the error info but as far as I can tell, either the MessageBox doesn't
appear or flashes quickly and disappears.

Thanks alot,
-Flack