VSTest task does not execute test dll(s) built for Platform x64

I am using Visual Studio Test task version 2 in my build definition in TFS 2017.Once my build is successful and it generates test dll(s),VSTest task is not able to run the test dll(s) that are built on platform x64.I am getting the following message:

Test run will use DLL(s) built for framework Framework45 and platform x86.Following DLL(s) will not be part of run: 'TestDllName.dll' is built for Framework FrameworkCore10 and Platform x64.

Has anyone faced this problem before??Please provide me suggestions to fix this.