It was in the same location which you had referred in your 1st reply. I donot know how I missed. When I searched for the first time, I had used "Find" with "reg678.dll" in the search box. The search didnot report any entry since I didn't know what was HKLM. Later, I undertood from a friend of mine and went to the registry and opened the location you had referred and found a long entry within which this was referred. After removing, it got solved.
Your first reply itself was the solution. Since I was not coversant with the abbreviated HKLM, I was groaping in the dark. After learning what it meant, I could understand your first reply.
A lot of thanks for your advice. After all people like you in AVAST won't be a novice like me.
I Once again thank you,
pscraja