Strange problem - Fast busy on SPA3102

I use a Linksys SPA3102 after a router. I use VOIPo for incoming and domestic outgoing calls and another provider (callwithus) for international outgoing calls. The configuration has been working for a few days without any problem. This morning, when I picked up my phone, I heard a fast busy tone. Rebooting the ATA didn't help. Strange thing is, I can still get incoming calls. Using the ATA VOIPo provided also eliminates the fast busy tone.

Do anyone has similar experience or have some idea what the problem might be? Thanks.

EDIT: It turns out this is re-order signal due to a bad dial plan.

- kjpus