Visual Studio 2017 failing to install nuget package in .NET 4.7 project

There is another reason for this error message by the compiler. While building , make sure the source code is placed at a folder location which is less than 260 characters long. For example, a path like C:\Users\User\source\Services\Exp\Sample-web-application-indot-net-displaying-RestAPI\Sample-web-application-indot-net-displaying-RestAPI\SportsStore is around 150 characters long but there are sub folders in the solution which in turn have source code files and so on. Sometimes the overall length of the path of some files breaches the 260 character length.

I think the future versions of Visual Studio would have a bigger length allowance. Until then, we can make sure that our file names are not too long.

OK, big Thank You @danmosemsft who suggested digging around with the SysInternals process monitor. After fiddling with it for a bit, I finally figured out how to narrow the result set to just file activity. What I noticed, and the nuget engineers should TAKE NOTE of this: The problem was NOT a too-long project name, rather, nuget was attempting to update a package that was no longer there. Why it went away is a mystery yet to be solved. I normally stay out of the packages directory and do not fuss with the packages.config file. I think that this might have to do with my impatience waiting for VS to start, load all the goodies and then allow me to perform a "Manage NuGet packages" - update all. I remember seeing an update to either NUnit or FluentAssertions that wanted to perform some additional file activity aside from just installing the next version, a script I believe. Can't speak to it with assurance, I wasn't paying that much attention as third party updates usually "just work". I didn't see the "finished" line from NuGet so I think that was the root of my problem. Rather than wait until VS has settled down, I pushed it a bit (hey, the buttons responded so there shouldn't be any problems...).

As a result, the packages directory was absolutely chock full of old stuff that did NOT belong there. So, I manually cleaned up all the cruft, manually cleaned up the packages.config file, restarted VS, waited for it to settle down, performed my NuGet updates and viola! no problem - HAVING NOT CHANGED ANY OF THE ANCESTRAL PACKAGE NAMES BY EVEN A SINGLE CHARACTER.

So, what do I conclude from this? It is my belief, and the guys that actually build nuget and nuget.server should take a closer look at the errors being thrown, such that I think that the error is not so much a path too long error, rather it's a "hey, I didn't find the file I expected so the file name is full of junk (and probably too long now) so I'll throw an error that says it's too long and quit". It's seemingly a failure to handle a missing package/package directory that is causing this particular problem

I solved my problem by ensuring that all the package directories were clean of all junk and rebuilding from a clean source. My problem is now solved.

Thanks to all of you that responded.

Update: While the above contributed to the solution, it was NOT the answer. Here is the sequence of events that led to this problem and it's ultimate resolution. The solution was created in the C:\User\Sam\Documents\Visual Studio 2017\Projects directory with the specified name of AWE.Lib.ADO.MsSqlSvr.ServerEntityHandler. This worked just fine, no errors. However due to a change in naming scheme from on high, the root directory for this project was changed from "C:\User\Sam\Documents\Visual Studio 2017\Projects" to "C:\User\Sam\Documents\Visual Studio 2017\Projects\DotNet_4.7\AWE 8.x". No problem, I thought - given that a co-worker who also happens to be a MS MVP had told me that all naming length restrictions had been removed in VS 2017. So...I moved the project from it's current home to the directory specified. Compiles just fine, brings in UPDATED BUT ALREADY INSTALLED nuget packages just fine, etc.

Or so I thought. When I needed to add a NEW (one that had not been a part of the solution before) nuget package to the mix, I received the above error. Turns out that the new name of the receiving solution is a few characters longer than VS will accept - the naming length restrictions are STILL IN PLACE.

How did I finally solve the problem: After struggling with this, I threw my hands up and decided to start all over again - a true File | New. So, I started with a new solution named as follows: "C:\Users\Sam\Documents\Visual Studio 2017\Projects\DotNet_4.7\AWE 8.x\AWE.Lib.ADO.MsSqlSvr.HndlrServerEntity" THIS GENERATES AN ERROR - name too long. I wondered at Nuget's error in that it specifies that the name should be less than 248 characters in length or 260 maximum.

What I am allowed to use iaw the new solution dialog is this: "C:\Users\Sam\Documents\Visual Studio 2017\Projects\DotNet_4.7\AWE 8.x\AWE.Lib.ADO.MsSqlSvr.HndlrServerEnt", for a total of 106 characters in length. If the directory is shortened, I can add to the length of the name. If I shorten the length of the actual solution name, again, VS'll accept it. So long as the total length of directory plus solution name is less than or equal to 106 characters, there isn't a problem.

The nasty bit comes from creating the solution in one location and having it work in all respects just fine, moving said solution to a different directory, still having it function in all respects (I did NOT need to add any new nuget packages yet), then trying to add a new nuget package to the mix after the move. THAT is what triggered the above nuget error.

So...the ultimate "fix", use a shorter name as it seems that 106 characters is the limit despite what the error messages are saying (and what the MS MVP was told/told me).