Recipient name not recognised in 5.5

Had to recreate corrupt mailbox and copy pst into new mailbox on exchange 5.5. Added mailbox to all distribution lists it was in. Now when creating a meeting and inviting distribution list (a) with this new mailbox in it get a message saying the recipient name is not recognised.
Can invite this person individually to a meeting and it works but not from the distribution list she is in. All other users in the list get the meeting invite OK. Have tried removing and adding person back into distribution list to ensure new mailbox is in list.
Mailbox alias is now different for the newly created mailbox.
Any help greatly appreciated.
thanks
Kath