I have found some related links but this does not apply to the issue I have:

http://blogs.msdn.com/b/tom/archive/2008/06/09/cannot-create-shadow-copy-file-name-when-that-file-already-exists.aspx
http://connect.microsoft.com/VisualStudio/feedback/details/227522/cannot-create-shadow-copy-variousfilename-when-that-file-already-exists

In my case, I am able to copy the new DLL in the bin directory. For, on all the hits in pending queue until the new DLL gets refreshed, some users might get the message. Like I said, this is new. I use the same procedure I have been using for two years and this just started recently after new updates on the server.