Can't install any NuGet Package if at least one Source is not available
This is by design. Since we support searching across multiple sources for the packages that you need, we need to be able to reach all sources and get the package results before restoring these packages, to be deterministic and consistent in the way we do restore.
However, we understand that some users go into offline/online modes and we are investing in building a feature set that will enable you to temporarily disable some sources while you are working offline. In the meantime you can look into creating a custom nuget.config that does not contain the offending source and using that to restore when you are in the offline mode.
This is an old question so I'm surprised the workaround from the bug report wasn't added here. To save reader a click:
- From within Visual Studio, open Tools -> Options -> NuGet Package Manager -> Package Sources
- Untick all of the package sources that are unavailable, leaving just
the public NuGet entries.
- Install your packages as normal
Once you're back in your office follow steps 1 and 2 again but this time make sure everything is checked.