I've had this happen many times and it was discussed a bit on the alt process mailing list a few months ago. You aren't alone. Make sure to add all of the silver nitrate then put the solution in a brown bottle let it settle for a few days. There will be some precipitate on the bottom but the solution on top will clear and, provided that the proportions are correct, it should work just fine. Some people filter out the precipitate but I leave it in the bottle and discard it when I reach the bottom. I've found that a lot of the excess silver will go into solution as the mixture ages.