Animation not working

hello all,

I have been having a problem with .fbx format export when compiling it to xna. When i export animated object it gives the following error: Error normalizing vertex bone weights. BoneWeightCollection does not contain any weighting values. From what I understand you need to apply weights to bones by somehow adding them to vertex groups( though I could be wrong) however I did not find any way to figure it out. Can somebody help? I am really really confused right now.