asterisk users - Jul 2006 - Help! Zap Startup failure: why is libpri not defined ?

Really sorry for the cross-posting, but I can't start my ISDN line at 
the moment :(

I checked out the latest version of * trunk (asterisk/zaptel/libpri) today.

Did the make clean / make menuselect / make / make install with no errors.

However, trying to startup * fails with the following:

[chan_zap.so] => (Zapata Telephony)
Jul  5 23:23:01 ERROR[21604]: chan_zap.c:10694 setup_zap: Unknown
signalling method 'pri_cpe'
Jul  5 23:23:01 ERROR[21604]: chan_zap.c:10305 setup_zap: Signalling
must be specified before any channels are.
Jul  5 23:23:01 WARNING[21604]: loader.c:785 __load_resource:
chan_zap.so: load_module failed, returning -1
Jul  5 23:23:01 WARNING[21604]: loader.c:847 print_and_load: Loading
module chan_zap.so failed!

tracking this down, seems to be in chan_zap.c, where pri_cpe is in a
block of code surrounded by an #ifdef HAVE_LIBPRI

#ifdef HAVE_LIBPRI
[snip]
   } else if (!strcasecmp(v->value, pri_cpe")) {
                                          cur_signalling = SIG_PRI;
                                          cur_radio = 0;
                                          pritype = PRI_CPE;
[snip]


so I can only assume that HAVE_LIBPRI is not defined. But why is it not
? Have I broken something in my system ?

Any clues would be gratefully received.