Maya's export skin weights is the worst feature in the package. It exports image files when the data it should be exporting is skin weights. If you don't have fantastic UV's you will not get the weights to save correctly, and even if you do have good UV's they wont save exactly how you painted them.
The solution to this is to use a script that saves the real weights as a text file.
Using the skinCluster and skinPercent commands you can get all the correct weights. Luckily there is a script on highend3d.com that will do this. I belive it is called saveSkinWeights.mel and it saves a text file with all the weights so you can load them back in correctly. It can also save weights on point position so you can change the vertex count. By this I mean a point at position XYZ has weight A, instead of vertex 1 has weight B.

Hope this helps. I took a looked at your earlier post and without seeing the maya file I can't see what your problem is, although I'm going to guess it's to do with your wrap deformer. Personally I never use wraps as they give you too many problem.

Richard