Don't take my rating as an indicator - I haven't played here a lot, it always is laggy to me (slow computer)
How did you select the candidate moves? Usually, you should look for both your plans and your opponent plans - do you know what he is planning? Can you see any weaknesses in your position (e.g. backward pawns that can be attacked) or does he have an advantage there (e.g. you have your pieces on the other side of the board and will take too long to reach the threatened side)? Is he trying to undermine something?
Either that, or they think up of some complex strategy that involves some fancy piece pushing. Or they are not playing the right moves. Chess, however, is an unpredictable game - if it was predictable, it'd be solved by now. Since you're playing correspondence, there is a LOT of time for players to find and formulate a plan, or moves. Always keep yours in mind, and try to guess their plans. Don't just ask their next move, ask their game plan.
Here's a question for the better players: can you generally predict what your opponent will do in a game, at least within a small set of 2-3 moves? Or do you quite often find yourself completely surprised? I'm not talking about obvious queen swap takebacks here, or the first 4 moves of the Ruy Lopez. I'm thinking that, when I play a correspondence game, in the middle or endgames, I *should* be able to predict the 2-3 best candidate moves of my opponent and plan responses. But I very frequently find myself either with absolutely no clue what he will probably do next, or else I find myself totally blindedsided by him taking the game in a totally unexpected direction. I'm curious if this is because I'mstill relatively new at this, or if this is really a characterstic of the game in general.