Cannot access a particular mailbox

I have had Freedom Essentials on my business phone for over a year.  I use 4 mailboxes.  Someone has left me a message in box #2, but no matter how hard I try, I cannot listen to the message.  I have created access codes for the mailbox, and a general access code.  I keep getting the recording, "To access mailbox #2, press 2".  When I press 2, it says "invalid entry".  I recall other times I had to rerecord the greeting, create new access codes, etc to access particular mailboxes, but I cannot find that option.  Please help.