It depends what you mean by solve. Scrabble, as a two-player game, has a significant branching factor compounded by the fact that the tile drawing makes it both a stochastic game as well as one with hidden information. Maven
http://en.wikipedia.org/wiki/Maven_(Scrabble) is an AI that can play Scrabble, and it's good, but it's certainly not "solved".
On the other hand, crossword puzzles are single-player games that use natural language wordplay to create a challenge. Some AI work has been done in this field, which can use a Web search engine (like Google) to try and determine the answer to each clue based on the clue (as well as any candidate words/letters already filled in). The hard part is understanding the clue. Look to systems like IBM's Watson to see how those kinds of problems can be solved.
"Solution" in a single player game, like a crossword puzzle, is solved in exactly one way: when all the rows and columns are filled with legal words (usually -- unless the author rigged it to allow clues to have multiple solutions, like the election day crossword in the NYT in 1996). A "solution" in a two-player game is when, no matter what move you make, your opponent knows perfect play. For example, checkers is solved: http://en.wikipedia.org/wiki/Chinook_(draughts_player)