Get the prime factorization of 2500: 54 * 22 or 5 * 5 * 5 * 5 * 2 * 2. There are six numbers so roll each 5 four times and 2 two times (for the six rolls) or roll 5 four times and roll 4 once as well as rolling a one. These are only possible combinations because 5 * 5 = 25 (bigger than six), and 5 * 2 = 10 (bigger than six). So 2 * 2 = 4 is the only other way to get another combination.
So there are 2 combinations, 5 5 5 5 2 2 = 6! / (4! * 2!) = 15 permutations, and 5 5 5 5 4 1 = 6! / 4! = 30 permutations.
So 15 + 30 = 45 different sequences of rolls. 
(Sorry for reposting the same solution Guest, but I thought he should know how you got the 2 different combinations just in case)
