asterisk users - Mar 2006 - I can't resume a call on hold from zap device

I have a strange problem: if I put on hold an incoming call from my Digium
TE110P, I can't resume it and the person at the phone continues to hear MOH
until the line falls.
My TE110P is connected with an italian E1 NT.
If I put on hold a call on a SIP channel I can resume it without any problems. 
 
Is there someone that can help me? 

These are my configurations: 
 
zaptel.conf 
 
span=1,1,0,ccs,hdb3,crc4 
bchan=1-15 
dchan=16 
bchan=17-31  
loadzone = it 
defaultzone=it 
 
 
zapata.conf: 
 
[trunkgroups] 
 
[channels] 
 
language=it  
signalling=pri_cpe 
switchtype=euroisdn 
usecallingpres=yes 
pridialplan=local 
prilocaldialplan=local 
nationalprefix=0 
internationalprefix=00 
faxdetect=both 
callwaiting=yes  
echocancel=yes 
immediate=no 
overlapdial=yes 
echocancelwhenbridged=yes 
echotraining=400 
callerid=asreceived 
group=1 
context=from-pstn 
channel => 1-15,17-31 
 
 
Thanks in advance, Marco.