Error message - The Vullnerability Protection Engine has been corrupted

Hi, I get this error when I start up my Macbook

 

Error message - The Vullnerability Protection Engine has been corrupted.... etc

 

Can someone tell me how to fix this error - I have a Macbook OS X 10.5

 

I have run a full virus scan already and it is still coming up with this error

 

Thanks!!