I am trying to weight paint a mesh for a unity game, and only a few if any of the vertices are being painted. This is something I was able to do a while back in version 2.49, but now it doesn't work. This is also affecting my ability to vertex paint. I just reinstalled blender, and have taken a screenshot of me weight painting a subdivided version of the default cube(Without subdivision it wouldn't paint at all.), And it is clear that only a few of the vertices are being painted. I am trying to complete a model for a client and this has absolutely halted any forward progress. Help would be highly appreciated, Thank you.
[EDIT] OS = windows 7, gfx card = gtx 780ti. I have tried versions - 2.69(released 2013) through 2.73(released 2015) All fail.