>>Unless you are installing the assembly in the GAC the application will use the assembly that is present in the relevant bin folder and, of course, you can't have too versions of the same assembly in the same folder.
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>Assemblies are located in the bin folders.
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>>In fact, if you intend just replacing the VB.NET assembly with the C# version in the bin folder, I think you will need to ensure the version numbers are the same.
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>>But if you change the reference in VS, build and deploy then the issue doesn't arise.....
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>I am looking at the minimal steps to convert a specific component. I guess, in order to avoid conflicts, I would need to use a temporary namespace and do a global replace at the very end once it is full tested, before releasing the final version with the required namespace.

Seems to me it would be less hassle if you stuck with the same namespaces and just changed the project references to point to the C# library project rather than the VB.NET one (you could have both projects in the solution with different names)