Updating package wtih nuget, installs fine, the reference is there, but when you compile, it says it's not there?

At work today, we had updated all out NuGet packages for our internal libraries.


I applied them to one of my solutions, a ton of projects...


most of them were fine... but for some of them, even though I could see the reference,
when I compiled it, it said the reference wasn't there.


Intelligence saw it, and my using statements were not RED..


WTF!


The answer of course is, assumptions...


Turns out, that the project in questions was referencing .Net4.0, and the Package referenced 4.5


there was even a yellow warning about it in my output window after the compile...
but who looks at those!(DOH)


I hope this saves someone else the pain...