Help me system recordings on freepbx 2.8

Hi,
i uploaded a file mp3 in freepbx 2.8 on centos 5.3 (asterisk now)

context:
[ivr-2]
include => ivr-2-custom
include => from-did-direct-ivr
include => app-directory
exten => #,1,Noop(Deleting: ${BLKVM_OVERRIDE} ${DB_DELETE(${BLKVM_OVERRIDE})})
exten => #,n,Set(__NODEST=)
exten => #,n,Goto(app-directory,#,1)
exten => h,1,Hangup
exten => s,1,Set(MSG=custom/prova_test)

prova_test is [[email protected] asterisk]# locate prova_test
/var/lib/asterisk/sounds/custom/prova_test.mp3

[[email protected] asterisk]# cat musiconhold_additional.conf
[default]
mode=files
directory=/var/lib/asterisk/mohmp3
[none]
mode=files
directory=/var/lib/asterisk/mohmp3/.nomusic_reserved

tail -f /var/log/asterisk/full

[Sep 21 15:56:11] VERBOSE[8137] logger.c: – Executing [[email protected]:11] Set(“DAHDI/1-1”, “__IVR_RETVM=”) in new stack
[Sep 21 15:56:11] VERBOSE[8137] logger.c: – Executing [[email protected]:12] ExecIf(“DAHDI/1-1”, “1|Background|custom/prova_test”) in new stack
[Sep 21 15:56:11] WARNING[8137] file.c: File custom/prova_test does not exist in any format
[Sep 21 15:56:11] WARNING[8137] file.c: Unable to open custom/prova_test (format 0x44 (ulaw|slin)): No such file or directory
[Sep 21 15:56:11] WARNING[8137] pbx.c: ast_streamfile failed on DAHDI/1-1 for custom/prova_test

why ? i crazy!!!
help me!

Your answer is right here:

MP3 is not a supported file type for system recordings.

This is the instructions on the systems recording page. Is this not clear?