No, there is no difference in meaning. In fact, the one word version makes no grammatical sense whatsoever. Putting the 'a' and the 'while' together is as nonsensical as saying 'It's been along time'. 'While' is a noun here, and so it should be preceded by the indefinite article 'a'. It is incorrect to join them together as if this were an adverb. You can just about see the logic in the adverbial use 'Wait awhile', but even this is doubtful. If you stick with the two-word version you will always be correct. A while.