Quote - I modeled and UV mapped the sweater for Alyson in Hexagon 2.5

Make sure you tick "Merge equal uvs" when exporting from Hexagon.

I suspect the "tabs in group names" that PhilC mentioned are because you have a hierarchy of objects, i.e. one or more levels of grouping showing in the Hex scene tree.
There are two strategies to cope with this, one is to open the OBJ file and replace all tabs with spaces (simple and probabl enough to stop Poser throwing a wobbly); the other is to save in Hex format, then flatten the hierarchy and export as OBJ, then reload the Hex file.

In either case avoid any spaces in any names used inside hex as they are treated as name seperators by OBJ file readers (which is why Hex is cheating by using tabs so that it can reconstruct the hierarchy, but which would appear to choking Poser's internals).