Salesforce Security Token:
A Salesforce Security Token is often required for authentication when Salesforce is not being accessed through a web browser.
To reset your security token, login to Salesforce.com and go to Setup > Personal Setup > My Personal Information > Reset My Security Token.
Click on the “Reset Security Token” button. Salesforce will send an email to the email address associated with your Salesforce account which will include the security token.
The security token will need to be appended to the Salesforce password when entering the Salesforce login information in the DataSynch Setup.