asterisk users - Jun 2005 - ring requested on channel 0/23 already in use on span

Anyone know what "ring requested on channel 0/23 already in use on 
span" means?

Happened this morning and locked up all inbound and outbound calls. Had 
to shutdown -r to repair it.

PRI
TE110P
CVS HEAD as of 05/24/05

Thanks in advance.
/rg