Integer types not allowed (at 'paddingLeft' with value '20')

I added some padding to a button and a textbox in Visual Studio for my Android app and I'm getting this error. Error 2 Integer types not allowed (at 'paddingLeft' with value '20'). c:\users\me\documents\projects\myapp\Resources\layout\login.xml 49.

I dont have a login.xml file but I do have a Login.axml file (I do realize that it is an xml file).

I started this project in Xamarin Studio then bought my licenses and now using Visual Studio. Am I not allowed to add padding to a button or textbox control from within the Visual Studio Properties window?