Hi,
I have the free version as well. I should put my specs on the signature part. That should speed up things.
Now back to you.
First off, right clicking on the A icon will not help in this case.
Here's what you do. Start avast. Look for the icon/button that says Virus chest. Click on it. Once there look for the problem file. Select it, then right click and choose extract. After this, select (browse if you will) the file that has been excluded from the scanner. Did this Help?