Fax not working

We are trying to fax both in and out of our PBX and not getting it to work we are getting the following error messages any help would be appreciated.

2015-02-13 15:33:56] WARNING[14557][C-00000007] func_channel.c: Unknown or unavailable item requested: ‘reversecharge’

[2015-02-13 15:33:56] WARNING[14557][C-00000007] pbx.c: No application ‘ReceiveFAX’ for extension (ext-fax, s, 4)