[Asterisk-Users] extension seen as busy when it is not

[James Armstrong]

Every few days our receptionist's phone will not take calls on one of 
the extensions. We have an extension 118 going to the first two lines of 
her phone and extension 101 going to the other. If we try to dial 118 it 
goes to voicemail even though she is not on the phone. Asterisk is 
thinking she is not logged on or something because the message in the 
log stays there is congestions calling that extension:

        >  dialparties.agi: extnum: 118
        >  dialparties.agi: exthascw: 1
        >  dialparties.agi: exthascfb: 0
        >  dialparties.agi: extcfb:
   dialparties.agi: Extension 118 has call waiting enabled2
   dialparties.agi: get_dial_string: extnum=[118]
     --  dialparties.agi: get dial string 118, SIP/118
     --  dialparties.agi: DbSet CALLTRACE/118 to 101
     -- AGI Script dialparties.agi completed, returning 0
     -- Executing Dial("SIP/101-dc56", "SIP/118|25|tTwWr") in new stack
   == Everyone is busy/congested at this time (1:0/0/1)
     -- Executing GotoIf("SIP/101-dc56", "0?s-CHANUNAVAIL|1") in new stack
     -- Executing GotoIf("SIP/101-dc56", "0?s-CHANUNAVAIL|1") in new stack
     -- Executing NoOp("SIP/101-dc56", "Sending to Voicemail box 118") 
in new stack


What can I look at to see why this is happening?

Thanks,
James