Salesforce has a plugin for Microsoft Outlook that is fantastic to use – called Outlook Connect. However when I first set it up – the login would fail and lock the user out.
In order to prevent this happening you not only need to enter the correct password into Outlook Connect but it needs to be followed (without spaces) by the security key.
The Security key should have been emailed to you by your administrator along with your password to login. However you can reset your security key by going to setup>My Personal Information > Reset your security token.
This will send an email to your email address with the security token that you can then copy and paste into Outlook Connect and it should work.