Are you using PhoneGap Build or building locally? I think the former, but I want to be sure.
We are using Build Server.
Now the build process is fixed for CLI 5.2.0, but for 6.3.0 still does not work!
And the 5.2.0 build is non-functional at the moment (although it is possible that this error consist now for about a month).
For winphone build cordova_plugins.js and plugins folder is completely missing in www folder (build process adds the script and the folder). I compared fresh new build and one month old build with the same input zip package.
Does your password have any special characters in it? I've seen reports on Google that caret (^) can mess things up a bit (this depends upon how the backend is coded, which I'm not familiar with).