It’s impossible to answer that question - there’s not enough information!
Are you trying to make a call at the time?
What other messages are coming up?
Set the verbosity of the asterisk console to 4 and you should get enough information.
When you’ve got that information, if it’s not obvious to you what the problem is, have a read of everything that might be relevant at voip-info.org/tiki-index.php?page=Asterisk
If you still can’t work it out, post a message here with enough information and someone may be able to help you.