would welcome any advise on dealing with this one
Welcome to the forum kmj098.
A little more information would be helpful. What is your operating system, and what is the name and location of the infected file? Is avast! unable to move this to the chest? What symptoms do you have?
Please try the free versions of AVG Antispyware
http://free.grisoft.com/doc/avg-anti-spyware-free/lng/us/tpl/v5
and A-Squared
http://www.emsisoft.com/en/software/free/
and let us know the results.