Error in script task in visual studio 2015

Hi All,

 we are facing a weird issue after an office upgrade to 2016.

the target ssis catalog is in 2014 where as we are building our projects in ssdt 2015 with deployment mode set to 2014 server.

what we did was , we removed office 2013 and installed office 2016.

now all our script task in ssis are not working and showing a error like 

SeverityCodeDescriptionProjectFileLine
ErrorSystem.IO.FileNotFoundException: Could not load file or assembly 'System.Collections.Immutable, Version=1.1.37.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.ST_83f5e20bfab4403f9e4c8fbf2d07b03bC:\Program Files (x86)\MSBuild\14.0\bin\Microsoft.CSharp.Core.targets67

SeverityCode DescriptionProjectFileLine
ErrorFile name: 'System.Collections.Immutable, Version=1.1.36.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' ---> System.IO.FileNotFoundException: Could not load file or assembly 'file:///C:\Program Files (x86)\MSBuild\14.0\bin\System.Collections.Immutable.dll' or one of its dependencies. The system cannot find the file specified.ST_83f5e20bfab4403f9e4c8fbf2d07b03bC:\Program Files (x86)\MSBuild\14.0\bin\Microsoft.CSharp.Core.targets67

we tried the solution like recreating the script tasks, but all in vain .

please help if you can .