Mirage 9 is compiled so that it is compatible with Java 6. This supports users who have old hardware that cannot be upgraded to Java 7 and/or they are running a very old version of jAlbum.
However a user who was (unintentionally) using Java 6 got an album generation error in Mirage 9 that indicated Java 7 is required. I don't know why this error occurred; maybe one of the 3rd party libraries requires Java 7.
So, Mirage 9.1 will force the Java version to be 7 or greater.