You are right, those calls are fake , as your McAfee security subscription is good until 04/21/2012. And to investigate on the scan error , please provide us with the below details :
Operating system > Windows Xp/Vista/7
Click on About in security center and let us know ;
McAfee Security center :
McAfee Virus scan :
Do you have any other security software installed on your PC ?
Open Interent explorer – Click on Help – Let us know
Cipher strength :