The error you're encountering is documented on the labs.aweber.com site.
You're getting that error because the findSubscriber method requires access to subscribers personal information (name, email, etc...) and your app has not requested access to subscribers personal information from the AWeber customer who authorized it.
AWeber API applications do not request access to subscribers personal data by default. You have to specifically check off that you want access to subscriber personal data before your application is authorized.
To correct this:
- log into the labs.aweber.com site and request access to subscriber personal data
- get a new access token for your app
- use that new access token and you should be able to find by subscribers.
Please refer to the documentation links below
As always if you have any questions please log into the labs site, click support and someone from the API support team will be happy to assist you.