Can someone please help me out here? I managed to enter avast 4.8 professional activation key but when it came to installing the downloaded updates it asked me for an update key. i tried this but it denied updates. Please i need the key. 
Welcome to the forums, stede50. 
Please modify your above post and remove the activation keys.
From where did you get your copy of avast?
@CharleyO-got it from my good friend but we broke our connection.i need help coz my virus d-base is outdated as my computer’s firewall reminds me all the time.
There are only a handful of places you can get a legitimate copy of Avast, starting Here. Whether you use the free (Home) version or purchase the Pro, the key would be emailed to you by the company at the email address you used.
Any other method of obtaining a key is not legitimate.
It is also possible your actual setup file for Avast is not legitimate, depending on the source. It would be worth checking.