First of all to see debug statements inside DebugView you need to compile your assemblies in "Debug" mode. For optimization reasons if you compile your assemblies in "Release" mode all the System.Diagnostics.Debug.WriteLine statements will be ignored by the compiler and you won't see any output in the DebugView.
When it comes to BizTalk project sometimes even though the tool bar will say the build is "Debug" as shown in the figure
When ...
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