Posting the same question to multiple forums is known as "Cross-Posting". Most forums (including this one), do allow it provided you follow the rules for doing so, which usually involves posting to the threads that you have also asked the question on other forums, and provide links to all of those threads.
Our policy can actually be seen in rule number 13 here: Forum Rules.
If you are not getting an answer here or elsewhere, and you have waited a reasonable amount of time (i.e. over 24 hours), no one is really going to be upset if you post it to another forum, as long as you do mention in both threads (on both forums) that you are doing so, and provide links to the other thread.
Trust me - I have been a Moderator on this forum for a long time. If you do that, people won't get upset. People get upset when people Cross-Post, and don't mention they are doing so and provide links. Or when people use the "Carpet Bomb" approach, and post the same question across a bunch of Excel forums all at the same time. It is generally recommend to post it to one forum, and give it some time to receive an answer before posting to other forums.
The link contained in the rule I referenced contains a real good explanation of the issue with Cross-Posting and not doing it the right way. It really just comes down to courtesy, and respecting the time and efforts of others.
By the way, on our forum, if you have not received a response in over 24 hours, you can also "bump" your own thread by replying to it yourself. This will bring it back to the top. Often times, it may be because people are not clear on the issue, so you may want to add more detail when you bump.