It's definitely the same fabric overlay - which is from Solstiss lace.
http://i337.photobucket.com/albums/n374/royalmb/mary/laceoverlay.jpg
The beading is quite unique. The dress underneath brings out the different colored beadings on the lace.
Princess Mary has also worn other Solstiss lace fabrics which are used by Julie Fagerholt for her Heartmade collection. She has a Heartmade skirt using Solstiss lace which she has used two different colored-linings/underskirts - blue and beige:
http://i337.photobucket.com/albums/n374/royalmb/mary/heartmadeskirtdifflinings.jpg
She also has a Heartmade dress made from Solstiss lace using different linings - beige and black:
http://i337.photobucket.com/albums/n374/royalmb/mary/heartmadelacedress.jpg
The current Solstiss lace collection has a similar pattern to Princess Mary's gown but with not so many colored beads:
http://i337.photobucket.com/albums/n374/royalmb/mary/747200GEO.jpg
http://i337.photobucket.com/albums/n374/royalmb/mary/747200GEO-long.jpg
The thing about Solstiss lace is depending on your lining, it really changes the look of the lace. This is from the current collection too with different backgrounds:
http://i337.photobucket.com/albums/n374/royalmb/mary/761731GKQ.jpg
http://i337.photobucket.com/albums/n374/royalmb/mary/761731GKQ-close.jpg
The Solstiss lace with beads are about US$900 a yard. Just from this, I think perhaps her gown from 2004 was altered to the one we see in the dinner in Vietnam.