We work with a lead partner who posts leads to our SF org. They receive the following error when creating a test lead:
Fields to send: FirstName=Bob&LastName=Flynn&Company=PMG&Phone=5615889339&email=no%40mail.com&Street=1234+Main+St&City=Delray&State=FL&Zip=33446&time_in_business__c=5&desired_loan_amount__c=10000&AnnualRevenue=100000&Lead_Type__c=Picklistphone&Monthly_Revenue__c=61-90&debug=1&LeadSource=Powers-LiveTransfer
Salesforce.com Lead Capture Interface Reason: We could not create this lead. Lead Capture Page: Not available. Record Information: AnnualRevenue = 100000 City = Delray Company = PMG FirstName = Bob LastName = Flynn LeadSource = Powers-LiveTransfer Lead_Type__c = Phone Monthly_Revenue__c = 61-90 Phone = 5615889339 State = FL Street = 1234 Main St Zip = 33446 debug = 1 desired_loan_amount__c = 10000 Email = email@example.com encoding = UTF-8 time_in_business__c = 5 If you have any questions, please click on Help & Training at the top right of any page within salesforce.com
I also had them try swapping the field ids (e.g. CF00NA000000A9K40 ) rather than API name for custom fields, but no luck. I was able to create this lead with these values using dataLoader so there shouldn't be any issue with validation rules. All the data types of the fields match the input type. AND I checked that the default lead creator has the default record type assigned that I'm expecting. This is meant to post to production, not the sandbox.
The only other thing I can think of us is needing to encode the email so @ doesn't appear as %40?