TextWriterTraceListener doesn't work

I have declaration in Class1.cs

TextWriterTraceListener l_tracer = new TextWriterTraceListener(@"c:\1.log");
Trace.Listeners.Add(l_tracer);
if i add in class1 Trace.WriteLine("bla bla bla"), all works fine. result appears in output window and in file.
problem when I add in class2.cs  Trace.WriteLine("bla bla bla"). Result appears in output window, but DOESN'T appear in file.
what's wrong?

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