This is a known but uncommon issue, and occurs primarily when someone resubmits the same form by using their browser's back button. The resolution is to check your Leads for a similar or identical lead created at almost exactly the same time. If identical, discard the email, if similar, edit the lead in Salesforce with the information in the email you wish to save.
More technical details are below.
We use a unique token to track every page visited, and record that token in Salesforce as a unique field. If a second lead is submitted with the same token, validation rules will prevent that token being saved in Salesforce, and you will receive an email with the information from this second submission.
In nearly all cases, this is duplicate information, and Salesforce has successfully recorded the initial lead submission, and has rejected the second submission.
- A visitor submitted a form on your website, and then used their browser's Back button to return to the previous form page and resubmitted the same form a second time.
- The Visitor double-clicks the form submission
In all of these situations, you receive all of the data from the visitor, though the second submission arrives via email. Please check the email against the recently created Leads. Usually the information is identical, though if it is different, save in Salesforce the more relevant information.
An example of the text in the email from Salesforce is below:
Salesforce could not create this lead because of the reason listed below. For more information about this error or help with Web-to-Case-Lead, please contact Customer Support. Reason: DaddyAnalytics__DA_Token__c duplicates value on record with id: 00Q7000000p1Da8 Lead Capture Page: Not available. Record Information: DaddyAnalytics__DA_Token__c = 1370444660790-9323132 DaddyAnalytics__DA_Web_to_Lead_URL__c = http://yourwebsite.com/contact-us/ company = Acme email = firstname.lastname@example.org first_name = test last_name = test oid = 00D7000000123aV To incorporate this lead into salesforce.com you can key in the data above. If you have any questions, please click on Support at the top right of any page within salesforce.com. Customer Support salesforce.com