HI Brennan,
I test Esri Maps for SharePoint 4.0 too. Then I have the same issue.
Here is a result fo my trial and error.
If you still get the same error message with configuring Esri Maps App Configuration correctly, please check the following steps.
I'm not sure that here is the correct solution, but I hope it can be of any help to you.
- On the Central Administration home page, in the Application Management section, click Manage service applications.
- On the Manage Service Applications page, Confirm Members section in the Secure Store target application "Esri Maps App Login".
- In the Members section, confirm the SharePoint Service Application account is added.
If the service application account is added in the members, Check also the followings.
- On the Central Administration home page, in the Application Management section, click Manage service applications.
- Click the Secure Store service application.
- In the Key Management group, click Generate New Key.
- Reset IIS.
Then you will see Esri Maps Web Part.
Best Regards,
Atsuhito.