Not exactly sure what you are trying to achieve here - but the 0x80070021 type errors usually indicate that there is a conflict in your config.
What exactly are you trying to achieve ?

I have had a non dnn application run happily with DNN, using the same bin folder, although the actual files were in a folder beneath, because there can only be one bin folder from my understanding with a .net site.

The fact you are running a .NET 2 site and a .NET 4 site makes me think the conflict lies there. 
What about you have two separate IIS instances - eg.. dnn site pointing to www folder A with .NET 4 setup with integrated and another IIS instance with .NET 2 setup pointing to folder A and see how that goes.  I am only guessing here but I just can't see how the setup where one app requires .net 2 and the other requires .net 4 can work together as they read different folders in the C/Windows.... framework so that in itself would cause a problem.

And of course none of what I said may work but like I said -I have had dnn running with another .net app and it worked quite happily together but they were both running .NET 2 and there was not an issue there. 

And after reading this again, I am not sure DNN likes being in a virtual directory instance - it prefers a domain directory.  Can your other app run in it's own virtual folder leaving dnn to run as a full domain?

Nina Meiers

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