I'm new to this game and I cannot get my sphere grid for Tidus to work. No matter where I 'move' to, it will not let me use any of my spheres! It doesn't make sense because I move to places connected to unactivated nodes, yet it will still not let me use my spheres to activate them! So basically, I am constantly wasting sphere levels by moving around. I have no idea where to move to! It makes absolutely zero sense, and this is only an issue with Tidus! Someone help me please!

It doesn't make sense because I move to places connected to unactivated nodes, yet it will still not let me use my spheres to activate them! [...] and this is only an issue with Tidus!
Faulty copy of the game? I don't have the HD re-release, but if you have that... You might want to give either of these options a try:

- Delete data
- Re-install
- Re-download

I had a similar problme tothis, I had to re-install

Try re-installing the game.