Hi gamline and welcome to the forums!
First of all, I've removed the attachment from your message as it contained all your sensitive activation information. Please, refrain from posting your serial number and private information on the forums in the future
Here are two download links for AutoCAD 2011. These links are temporary and will expire in 48 hours:
AutoCAD 2011 32 bits
I've had a look at the serial number that was on your attachment and it is indeed coming back as invalid. Was this software purchased from Autodesk directly or from one of our official authorized resellers?