For some reason, I think I have seen this error message before but I don't remember the fix.
UC_520(config)#application
UC_520(config-app)#service fax_detect flash:/bacdprompts/app_fax_detect.2.1.2.3.tcl
UC_520(config-app-param)#param prompt flash:/bacdprompts/en_Uone_listen-first.au
Warning: parameter prompt has not been registered under fax_detect namespace
UC_520(config-app-param)#param mode listen-first
Warning: parameter mode has not been registered under fax_detect namespace