Unfortunately, I couldn't tell any specific issue. What I'm worried is the unforeseen issues that may come out during development. I haven't personally tried using Entlib 3.1 into a .NET 4 App. Also note that Entlib 3.1 is already in the list of
the Retired Releases of Entlib therefore support is somehow would be a little hard to get.
As for recompiling Entlib 3.1 in .NET 4 that may look like a lot of work rather than using EntLib 5.0 instead. Anyway, personally there's a lot of good stuff on Entlib 5.0 that is way better than Entlib 3.1, you may want to consider that as well. Hope
this helps :o).
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