The Partner Mail VS system's default configuration is 10 mailboxes, so it looks like the voicemail system does not recognize the new expansion card.
Try putting the old card back in and see if the system reverts back to a 20 mailbox arrangement. If so, the new card is bad. If the system no longer recognizes the original card then the voicemail module has gone bad.
If the voicemail module is bad, it might be worthwhile to upgrade to the Avaya Partner Messaging platform. More voicemail boxes, more recording time, more features (but a bit more expensive).