I can think of three approaches you could use:
- Leave a comment to the original poster. If you are lucky he will see it and update the answer. It might take a while though, and he may be too busy to reply.
- Post a new question linking to the existing one and asking for more detailed information about your specific problem. Show what you've tried and what error you got. This allows anyone to help you, not just the original poster.
- Leave a bounty on the original question to increase attention and encourage better answers that include the information you need.
You might find that option 2 gets you the specific answer you want the fastest.