I was getting similar errors and I had to add in the Prop.java class "(required = false)" on some elements.
Example:
@Element (required = false)
private Resourcetype resourcetype;
@Element (required = false)
private String creationdate;
@Element (required = false)
private String getlastmodified;
@Element (required = false)
private String getetag;
@Element (required = false)
private String getcontenttype;
In your case it looks like you have propstat defined in both the Response.java and Propstat.java. Maybe rename one of those to just "prop".