On your User Manual for MEGAN V6.4.12 page 14, there is “The File-- Meganize DAA Files… item: Opens dialog for meganizing one or more Diamond DAA files.”, but when open your MEGAN V6.4.12 July 5 2016 edition, there is no such option under File".
Please update to 6.4.13 to find this feature now also in the Community Edition (it was previously only in the Ultimate Edition)