Hi,
If Topo 2M is not working that means there's a problem decoding .GIF files on your system. 2M, 8, 32 and 256 are GIF (the rest are jpeg). 8, 32 and 256 are turned off by default since they are somewhat redundant (and gifs are slower to decode anyway).
2M maps are also redundant (they are the same base maps as 4M). However, they are gif and better resolution so in some cases they are nice to have.
My first suggestion is to check your screen depth. Some video cards don't work with our gif library (Corona) if they are in 16 bit screen depth mode. Try switching to 32 or 24 if so.
Easiest thing to do is just turn of Topo 2M so you can zoom in all the way on Topo 4M.
Let me know if any of this helps.