I've upgraded to 2.7 and I still run into the same issue....the exception is slightly different but appears to be mostly the same:
System.Net.WebException: The remote server returned an error: (404) Not Found.
at System.Net.HttpWebRequest.GetResponse()
at NuGet.RequestHelper.GetResponse(Func`1 createRequest, Action`1 prepareRequ
est, IProxyCache proxyCache, ICredentialCache credentialCache, ICredentialProvid
er credentialProvider)
at NuGet.HttpClient.GetResponse()
at NuGet.RedirectedHttpClient.GetResponseUri(HttpClient client)
at NuGet.RedirectedHttpClient.EnsureClient()
at System.Lazy`1.CreateValue()
at System.Lazy`1.LazyInitValue()
at System.Lazy`1.get_Value()
at NuGet.MemoryCache.GetOrAdd[T](Object cacheKey, Func`1 factory, TimeSpan ex
piration, Boolean absoluteExpiration)
at NuGet.RedirectedHttpClient.get_CachedClient()
at NuGet.RedirectedHttpClient.get_Uri()
at NuGet.DataServicePackageRepository.get_Context()
at NuGet.DataServicePackageRepository.Search(String searchTerm, IEnumerable`1
targetFrameworks, Boolean allowPrereleaseVersions)
at NuGet.PackageRepositoryExtensions.Search(IPackageRepository repository, St
ring searchTerm, IEnumerable`1 targetFrameworks, Boolean allowPrereleaseVersions
)
at NuGet.AggregateRepository.<>c__DisplayClass2f.<Search>b__2e(IPackageReposi
tory r)
at System.Linq.Enumerable.<>c__DisplayClass12`3.<CombineSelectors>b__11(TSour
ce x)
at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
at NuGet.AggregateQuery`1.GetSubQueries(Expression expression)
at NuGet.AggregateQuery`1..ctor(IEnumerable`1 queryables, IEqualityComparer`1
equalityComparer, ILogger logger, Boolean ignoreFailures)
at NuGet.AggregateRepository.CreateAggregateQuery(IEnumerable`1 queries)
at NuGet.AggregateRepository.Search(String searchTerm, IEnumerable`1 targetFr
ameworks, Boolean allowPrereleaseVersions)
at NuGet.PackageRepositoryExtensions.Search(IPackageRepository repository, St
ring searchTerm, IEnumerable`1 targetFrameworks, Boolean allowPrereleaseVersions
)
at NuGet.Commands.ListCommand.GetPackages()
at NuGet.Commands.ListCommand.ExecuteCommand()
at NuGet.Commands.Command.Execute()
at NuGet.Program.Main(String[] args)