NuGet.targets error : '.', hexadecimal value 0x00, is an invalid character after upgrade to .Net Core 2.1.1

after upgrade to .Net Core 2.1.1 I got this error:

  C:\Program Files\dotnet\sdk\2.1.301\NuGet.targets(114,5): error : An error occurred while retrieving package metadata for 'System.IO.4.3.0' from source'C:\Program Files\dotnet\sdk\NuGetFallbackFolder'.     C:\Program Files\dotnet\sdk\2.1.301\NuGet.targets(114,5): error :   '.', hexadecimal value 0x00, is an invalid character. Line 1, position 1. 

not able to solve it using

nuget.exe locals -clear global-packagesnuget.exe locals -clear packages-cachenuget.exe locals -clear http-cache

or

nuget.exe locals -clear all

thanks for any help