2017.2f3 problems opening project in VS community edition -.NET version related

Reinstalling Unity on a new PC - it added VS Community edition. Opened a previously working (in VS) project and get a bunch of errors about not having .Net 4.6.1 installed. The dialog directs you to download that version but it won't install because (surprise!) it's already installed.

Another option is to change the project to 4.6.1.

Another option is to not load the project.

Whichever option I take, the c# file I was trying to look at will appear in the editor, but all the parts of the Unity project that normally get loaded by VS do not get loaded. So intellisense, go to definition, find all calls to this function, etc. do not work.

I am using the (experimental) .net 4.6 setting in the "Player" preferences. This all worked properly in the 2017.2 betas but now ... not at all. I really can't go back to the normal setting for this without a lot of re-coding.

Here's an image of one of the several similar dialogs VS throws up when I try to open the project. I hope this is just some pilot error on my part!

 

Just in case anyone comes across this - here's the solution. It's NOT that you need 4.6. You need the symbol and intellisense info.

https://www.microsoft.com/en-us/download/details.aspx?id=48136