When trying to add new Campaign Member records to a Campaign (i.e. such as when going through the Add Campaign Members wizard in Salesforce), you might see an error message that says "Record type unavailable" after trying to add the Campaign Members. Typically, the reason for this is that you may not have completed the full Soapbox Mailer installation process yet (found in our Getting Started With Soapbox Mailer guide), and your Campaign Member object doesn't have a default Campaign Member record type set.
Here's a few troubleshooting tips.
1) Ensure that you have a default Campaign Member record type set
Go to Setup > Administer > Manage Users > Profiles > (select a profile) > Object Settings > Campaign Members > Edit. On the right side of the screen, select a default record type, and click the Save button.
2) Ensure that you've created the Soapbox Mailer Campaign Member record types
Follow the instructions in section 2 of the Getting Started With Soapbox Mailer guide to ensure you have the proper Campaign Member record types created. After completing this, you may want to go back to #1 above and set "Default" as your new default Campaign Member record types.