That location may not be correct.
Check the properties for Microsoft.SqlServer.ScriptTask & check the path.
The path to the Microsoft.SqlServer.ManagedDTS DLL should be in the same folder as this, I think.
To make the change, you'll have to delete the reference and then add it again.
If you haven't even tried to resolve your issue, please don't expect the hard-working volunteers here to waste their time providing links to answers which you could easily have found yourself.