You've attempted to select Primary as a key
option in the Key Definition window, but the table for which this
key is being created already has a primary key.
Use one of the following solutions:
Unmark the Primary key options for the
current key. You can still mark the Create Index and Unique options
for this key.
To replace the original and use the
current key as the primary key, save the current key with the
Primary option unmarked. Open the key originally defined as the
primary key and unmark the Primary option. Reopen the key you want
to make the primary key and select the Primary option.