Are you sure you have an error here?
What your API request should have done is to initiate a batch upload process (ie, a job). The result you show above seems to show that a batch job ("a07e2dywal2fmypyuak") was initiated and is in the "PENDING" status (jobs are scheduled, they go from PENDING, TO running, to completed).
To determine the status of the batch job, or to look at detailed results, pursue the link provided:
http://api.constantcontact.com/ws/customers/username/activities/a07e2dywal2fmypyuak
or simply login to your account, and go to Contacts/Activities and see if the job you submitted via the API is listed (and if the contacts were added).
Does this work for you?
Thanks,
Tom M
Group Product Manager – Content Editing
Constant Contact