Line constantly busy with Asterisk 1.4.26, Motorola Wildcard X100P

I’m having a problem where, as soon as I start Asterisk, the analog line connected to my Digium Wildcard X100P FXO card goes dead. When Asterisk is not enabled, if I reset the wall plug (by unplugging and replugging the analog cable), the analog phone connected through the pass-through port works fine. Once Asterisk starts up, it starts emitting an error-style tone on the analog phone, then goes completely silent. If I try to dial out, I get an “all trunks are busy” error message.

I’ve tried different variations of loop start and kewl start signaling, turning on/off reverse polarity busy detection, and a couple other tweaks (I don’t know many). Nothing seems to help. Does anyone have any ideas on what might be going on? I’ve collected all of the information I could think to collect below.

dmesg (relevant excerpt):
asterisk debug log:

lspci -v (relevant excerpt):
05:04.0 Communication controller: Motorola Wildcard X100P
Subsystem: Efar Microsystems Device 0001
Flags: bus master, medium devsel, latency 64, IRQ 16
I/O ports at dc00 [size=256]
Memory at efabf000 (32-bit, non-prefetchable) [size=4K]
Capabilities: [40] Power Management version 2
Kernel driver in use: wcfxo
Kernel modules: wcfxo

lsmod (relevant excerpt):
ztdummy 11352 0
wcfxo 19232 0
zaptel 205860 2 ztdummy,wcfxo

cat /proc/interrupts (relevant excerpt):
16: 164563147 0 IO-APIC-fasteoi wcfxo

Asterisk 1.4.26
kernel 2.6.28-14-generic
Ubuntu 9.04

general instructions followed to build Asterisk:

zaptel build failed, per this bug:

used zaptel source from repository referenced in bug post:

Thanks for reading.