i had experience on asteriskNow distro and often fighted with the faxoverip reliability
i compiled spandsp and also rx_fax and tx_fax with the same errors but they where working anyway
check the spandsp lib version in use is correspondig to the apps and check the asterisk makefile patching procedure
http://www.asteriskguru.com/tutorials/spandsp.html
using app_rxfax.c, app_txfax.c and apps_makefile.patch
maybe same patching procedure will work for ubuntu
i had experience on asteriskNow distro and often fighted with the faxoverip reliability
i compiled spandsp and also rx_fax and tx_fax with the same errors but they where working anyway
check the spandsp lib version in use is correspondig to the apps
and check the asterisk makefile patching procedure
http:// www.asteriskgur u.com/tutorials /spandsp. html
using app_rxfax.c, app_txfax.c and apps_makefile.patch
maybe same patching procedure will work for ubuntu