This error is caused by not having any packages setup for the account type they selected. For example, if they signup as a Single Listing account type and there are no packages setup, they will get this error.
The multi-listing account type also has different packages, so if you have packages added for the single listing account type, but not the multi-listing account type, then someone signing up for a multi-listing account will get this error, since there are no packages setup for the selected account type.
You can add packages from your Website Admin in the FS Control Panel under Items & Packages. See additional articles in this support category on how to add packages.