Wi-Fi sync problem

It sounds like you've done everything you're supposed to. Here's PC Mag's steps to get it going. I'd go through them again just to make sure.

How to set up iTunes Wireless Sync

1. Make certain that your computer and iPhone, iPad, or iPod touch are connected to the same Wi-Fi signal.

2. Connect your iPhone, iPad, or iPod touch to a Mac or PC via USB. Launch iTunes if it doesn’t do so automatically.

3. Highlight your iDevice in the sidebar.

4. Click "Summary" in the menu bar. Scroll down to the "Options" section.

5. Check the "Sync with this (iOS device) over Wi-Fi" box. Click "Apply."

6. Detach your iPhone, iPad, or iPod touch.

7. Initiate an iTunes Wi-Fi Sync by tapping Settings > General > iTunes Wi-Fi Sync > Sync Now on your iPhone, iPad, or iPod touch. Or, plug it into an outlet.

I'd also try restarting your iTunes and/or computer a couple of times.

Especially if your on a Windows machine.

The Apple Mobile Device service that runs in Windows is just all out crappy. I occasionally have to restart iTunes or my computer because it just stops allowing my devices to sync at all.

I figured that you've already tried this, but I thought I suggest it to be safe.