Cannot update the column information in table parse.com

I have a table lets call "Post" which has 3 columns "UserA"<ParseUser>, "UserB" and "Status"<String>. Data consists of UserA currentUser, UserB another ParseUser, status => A When I am going to update the status from "A" to "B" it throw me error

com.parse.ParseException: java.lang.IllegalArgumentException: Cannot save a ParseUser that is not authenticated.

Can anyone help me please?