NBU encryption keys

when i tried to create a new encryption key on NBU master (7.5.0.6), i got an error message saying "reach the encryption key maximum". this is the first time we see that. we have two encryption keys applied (encryption (legacy DES-40-bit), encryption (legace DES-56-bit)). do we have to buy more and how VERITAS count the encryption keys? we are using the encryption for all of our tape drives. usually we create a new key every new quarter, looks so far we have 7 keys created.

thanks in advance.