Dial to LOCAL fails

I am having trouble using DIAL to a LOCAL channel. The idea is that from an AGI script I call LOCAL/XXXXXXX to place a call. If I use this method to call an internal extension, all works fine. However, when I use DIAL to call LOCAL/9xxxxxxxxx where this should trigger a call to a DAHDI trunk, I get the following error on waitstream core. Any ideas?

(I’ve x’ed out the actual number…)

-- Executing [s@dial-pstn-helper:2] Dial("Local/9xxxxxxx@dialplan-siegel-bb3a;2", "DAHDI/1/19xxxxxx,60,tTkK") in new stack
-- Called 1/19xxxxxxxx
-- DAHDI/1-1 answered Local/91xxxxxxx@dialplan-siegel-bb3a;2
-- Playing 'siegel/Airport_Paging_Short' (escape_digits=) (sample_offset 0)

[May 26 09:05:39] WARNING[12317]: file.c:1240 waitstream_core: Unexpected control subclass ‘-1’
== Spawn extension (dial-pstn-helper, s, 2) exited non-zero on ‘Local/9xxxxxxxxx@dialplan-siegel-bb3a;2’