Error in Playback() and Background() in Asterisk or what?

[size=18]Hi all, I 'm a newbie in studying asterisk, I want to a start with “hello world” programe.
I use a X-lite softphone call to Asterisk server and server 'll play a sound file but I 've get a problem[/size]:

[Sep 14 12:16:08] WARNING[6115]: file.c:568 ast_openstream_full: File custom/1.wav does not exist in any format
[Sep 14 12:16:08] WARNING[6115]: file.c:871 ast_streamfile: Unable to open custom/1.wav (format 0x4 (ulaw)): No such file or directory
[Sep 14 12:16:08] WARNING[6115]: pbx.c:5714 pbx_builtin_background: ast_streamfile failed on SIP/1001-081d0ab0 for custom/1.wav
– Executing [101@phones:3] WaitExten(“SIP/1001-081d0ab0”, “”) in new stack
== CDR updated on SIP/1001-081d0ab0
– Executing [2@phones:1] Playback(“SIP/1001-081d0ab0”, “custom/agent-alreadyon.gsm”) in new stack
[Sep 14 12:16:15] WARNING[6115]: file.c:568 ast_openstream_full: File custom/agent-alreadyon.gsm does not exist in any format
[Sep 14 12:16:15] WARNING[6115]: file.c:871 ast_streamfile: Unable to open custom/agent-alreadyon.gsm (format 0x2 (gsm)): No such file or directory
[Sep 14 12:16:15] WARNING[6115]: app_playback.c:437 playback_exec: ast_streamfile failed on SIP/1001-081d0ab0 for custom/agent-alreadyon.gsm
== Auto fallthrough, channel ‘SIP/1001-081d0ab0’ status is ‘UNKNOWN’[quote]

These are my configuration file:
extension.conf:
[phones]
exten => 101,1,Answer()
exten => 101,n,Background(custom/1.wav)
exten => 101,n,WaitExten()

exten => 2,1,Playback(custom/agent-alreadyon.gsm)
exten => 3,1,Playback(custom/vm-theperson.gsm)

sip.conf
[1001]
type=friend
context=phones
host=dynamic
[1003]
type=friend
context=phones
host=dynamic

[1002]
type=friend
context=phones
host=dynamic

iax.conf
[general]
autokill=yes
[1001]
type=friend
host=dynamic
context=phones
[1002]
type=friend
host=dynamic
context=phones
[1003]
type=friend
host=dynamic
context=phones

help me, please![/quote]