I am trying to restore the missing nuget packages and it keeps giving me this Error:
An error occurred while trying to restore packages. Please try again.
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For me I cloned a solution (vs2015/NuGet3.4) that had a nuget dependency on a pre-release package that had been superceded. Nuget failed to restore the pre-release and wouldn't let me either uninstall or upgrade it. I frigged it by manually editting packages.config to target an older non-pre-release of the package, which I could then upgrade to the version I wanted. HTH