The address book is already connected to another Fullcontact account. Please contact support for assistance.
This notification usually means that the account you're trying to connect is already associated with another FullContact account. Since one contact source can only be associated with one FullContact account, you aren't able to connect it twice.
If you have created multiple accounts accidentally, we simply suggest deleting one of them. After that, you should be able to connect the address book which returned this error without any issues.
To delete the accidentally created FullContact account, go here -> Close Account.
You've reached the contact limit for your account.
To explain a bit, FullContact has a strict storage limit of 25,000 contacts per account. This is implemented due to the storage limit for personal accounts in Google which you can see here. We've adopted that limit since it significantly simplifies our syncing system for the challenge of syncing across Google, iCloud and Exchange accounts.
When you have exceeded your limit of contacts, you will get a notification in your FullContact address book letting you know. A few features will also be disabled when going over your limit - when over your limit you will not be able to add additional contacts or sources.
To remove this limitation, I'd suggest deleting specific contacts (feel free to use our smart tags to filter out contacts without email addresses / phone numbers) or disconnect contact sources (Twitter, Xing, LinkedIn).