A previously working on-premises TFS 2015 (with update 1) fails all builds that have nuget packages in them. The build log shows:
MSBuild auto-detection: using msbuild version '14.0' from 'C:\Program Files (x86)\MSBuild\14.0\bin'.
Restoring NuGet package StyleCop.Error.MSBuild.1.0.0.
Restoring NuGet package Microsoft.Diagnostics.Tracing.EventSource.Redist.1.1.28.
Restoring NuGet package Microsoft.Diagnostics.Tracing.EventRegister.1.1.28.
Restoring NuGet package Microsoft.Diagnostics.Tracing.EventSource.1.1.28.
Restoring NuGet package StyleCop.MSBuild.4.7.50.
Restoring NuGet package Newtonsoft.Json.8.0.3.
Restoring NuGet package Dapper.1.42.0.
Restoring NuGet package FluentAssertions.4.2.2.
WARNUNG: Unable to find version '1.1.28' of package 'Microsoft.Diagnostics.Tracing.EventRegister'.
WARNUNG: Unable to find version '1.0.0' of package 'StyleCop.Error.MSBuild'.
WARNUNG: Unable to find version '1.1.28' of package 'Microsoft.Diagnostics.Tracing.EventSource.Redist'.
WARNUNG: Unable to find version '1.1.28' of package 'Microsoft.Diagnostics.Tracing.EventSource'.
WARNUNG: Unable to find version '1.42.0' of package 'Dapper'.
WARNUNG: Unable to find version '8.0.3' of package 'Newtonsoft.Json'.
WARNUNG: Unable to find version '4.7.50' of package 'StyleCop.MSBuild'.
WARNUNG: Unable to find version '4.2.2' of package 'FluentAssertions'.
Unable to find version '4.2.2' of package 'FluentAssertions'.
Unable to find version '4.7.50' of package 'StyleCop.MSBuild'.
Unable to find version '1.1.28' of package 'Microsoft.Diagnostics.Tracing.EventRegister'.
Unable to find version '8.0.3' of package 'Newtonsoft.Json'.
Unable to find version '1.42.0' of package 'Dapper'.
Unable to find version '1.1.28' of package 'Microsoft.Diagnostics.Tracing.EventSource'.
Unable to find version '1.1.28' of package 'Microsoft.Diagnostics.Tracing.EventSource.Redist'.
Unable to find version '1.0.0' of package 'StyleCop.Error.MSBuild'.
Unerwarteter Exitcode 1 vom Tool NuGet.exe zurückgegeben
On dev PCs the solutions build just fine and nuget packages are restored without problems.
How to fix this?