As it currently stands, it is:
Questions must contain working code for us to review it here. For questions regarding specific problems encountered while coding, try Stack Overflow.
That kinds of just redirects the users to SO, which is good. But it is like saying goodbye. Wouldn't it be better to make it like this:
Questions must contain working code for us to review it here. For questions regarding specific problems encountered while coding, try Stack Overflow. After your code is working you can edit this question for reviewing your working code.
It is like saying, "go there to fix this, and then come back and we'll help you." It can have a good impression on new users and may help with getting some users back from SO after getting their code corrected.
How about that?
Update
I tweaked it a bit:
Questions must contain working code for us to review it here. For questions regarding specific problems encountered while coding, try Stack Overflow. After your code is working you can edit this question for getting a code review.
Update 2
Just thought to add the link of Stack Overflow to the message after I found myself adding it in a comment because the user was new and didn't have an account on Stack Overflow. I thought he might be left wondering why he would overflow the stack if he hadn't known that a site with that name existed.
Questions must contain working code for us to review it here. For questions regarding specific problems encountered while coding, try Stack Overflow. After your code is working you can edit this question for getting a code review.