The UpLead integration supports the Salesforce API, which is only available with the following versions:
Enterprise Edition
Unlimited Edition
Developer Edition
Performance Edition
Salesforce Contact, Group or Professional versions do not allow the use of an API. If you are currently using any of these versions, you can either download your leads to microsoft excel and upload to Salesforce or you can upgrade your Salesforce account to any of the supported Salesforce editions above.