You may have arrived here because you clicked the Add People menu item. If so, then your Administrator has disabled this item. To add a new person, you should do so in the right context.
The various places you would add a person to the database are the following:
Here are some instructions on proper searching (before adding a new record). These are designed to prevent adding duplicate records to your database. Click HERE
NOTE: If you are adding a new record because the person made a Membership Decision, you would want to add them first as a Visitor to the meeting at which they made this decision. Then you can record their decision.