I have seen duplicate words in print frequently, but usually with words like "had" rather than "to". For example: "If Joe had had a better instructor, he would have passed the test." Such sentences can be a little hard to read, but in general there is no rule against it; the construct is grammatical. Often a reader will have the same reaction as an automatic spell checker -- "This must be a typo" -- only to re-read and see that it actually does make sense.
There seems to be a case for the notion that "had had" is more acceptable than "to to". In print, it's probably best to avoid "to to", but when spoken, I really don't see a difference regarding the level of awkwardness or clarity. For example:
Person A: I'm really not in the mood to run the mile right now.
Person B: But you have to to make the team!
Spoken with proper tone of voice, I think this usage is perfectly acceptable and understandable.
In general, I would consider rewording the sentence to make it flow better, on a case-by-case basis. Here is an article provided by Grammar Girl discussing usage and correctness in more detail.