Check that you have not made a replica of the database using Microsoft Access. A replica can not assign numbers to the items you are adding to the database. A replica can also be made if you drag a database in to My Briefcase. You need to find the original database and use this is as your IRRICAD working database in order to be able to add new items.
Note a replica can also occur if you have your working database on a network drive. Server back-ups can cause replicas of Access databases.