"Merge point" merges every selected point within a user defined radius (the default is huge when seen in terms of Poser scaled items). The problem with doing this on a thin but solid model like yours, with front and rear facets separated by a tiny gap, is that you're likely to merge the front and rear facets by accident. The way to tell if you have separate vertices occupying the same spot is to use a single vertex selection, then move it. If some of your mesh moves but another vertex stays on the same spot, then there's your problem. If the separated vertices have identical 3D co-ordinates, then UVmapper's "weld vertices" command will fix it for you. If the vertices are really separated, if only by an infinitesimal amount, that won't work. Sometimes you can scale the model down by (say) 100 or 1000 times, then back up again, which will round off some of the precision in the coordinates and enable you to weld vertices. Of course you need to pick a scaling factor which doesn't bend your model out of shape. I have even resorted to an Excel spreadsheet to achieve this. Try "weld vertices" and let me know how you get on.