title: Why would I get "Not a valid keystore file" error
body: <p>I'm trying to set up an android build in Visual Studio App Center, but when trying to upload our keystore file I get the error "Not a valid keystore file". Could anyone think of a reason this could be happening? I have manually created a new keystore and that one seems to work. I can't use this though because its an existing app and would force users to uninstall and reinstall the app. </p>
  
  <p><a href="https://i.stack.imgur.com/5aXTj.png" rel="noreferrer"><img src="https://i.stack.imgur.com/5aXTj.png" alt="enter image description here"></a></p>