Avast anti virus stops programs running

Hi
I am finding that a number of applications will not run, so far this has included Adobe acrobat reader, excel and word. The timer circle just disappears after a short while, no error is given. Each time it happens I can fix it by running the Avast repair function.
How do I stop this happening?

  • Which Avast…? (Free/Pro/IS/Premium)
  • Which version…?
  • OS…? (32/64 Bit…? - which SP/Build…?)
  • Other security related software installed…?
  • Which AV(s) did you use before Avast…?