Sync – Bitcoin payment not received. What does it mean when a client is syncing?

This is probably normal. “Synchronizing with the network” really means “downloading the blockchain,” which can take anywhere from a few hours to a day.

After “catch-up” you should see how many blocks have already been downloaded. At the time of this writing, there are 220,000 blocks, which will be fully synced when reached. If the numbers continue to increase, you’re probably heading in the right direction.

You can speed things up a bit by forwarding port 8333 on your router (it’s not that important if you don’t know how to bother).