Had this same problem, but I found the solution. Meshlab doesn't like spaces in file names. I changed my file names so they had no spaces, and it imported correctly.

You will have to open up both the .obj file and its associated .mtl file in Notepad or another text editor. Change the references they have. There should be three files associated witht he object: a .obj, a .mtl, and a .png. The .obj references the.mtl and the .mtl references the .png. You have to change the names of all three, and also the name of the .mtl referenced within the .obj + the name of the .png referenced within the .mtl.

Hope that fixes it for you.