Blender weird invisible seams...can't be removed

Hi. I am trying to map a dress but the problem is that there appears to be an invisible seam, actually two, that won’t let me make a single shell from two. While making the dress, I separated by selection some parts, put them in other layer, added solidify on them, marked seams, brought them back in the original layer, Joined them with the rest of the dress and removed doubles. After that, marked again some seams and unwrapped. Now I can’t get rid of the invisible seams. Also, I have provided here a link to my dress to see what is the problem…

http://www.pasteall.org/blend/25298

Could you help me please?