Cannot create custom data field in Mambo Civicrm

I have uploaded both the 2604 and the 2570 versions of Civicrm separately into Mambo. When I try to create extra custom fields (in this case, county and congressional district fields - alphanumeric, select), it doesn't allow me the option to save changes. In fact, when I look at the sandbox version of Civicrm on openngo.org, it presents a longer list of options for adding a custom field.

I am using Moxilla Firefox as my browser and Mambo 4.5.2

Thanks.