sat,
rar have caused some problems for Avast.
You can try to "exclude" scanning of rar files to determine if that is the cause.
Open up the GUI (interface)......
Menu....
Settings.....
Exclusions......
then click "add". Enter *.rar and Okay
Try the scan again.
Regardless of result, go back over steps, but this time use Remove and take out *.rar
Once we know for sure that the rar file is causing problems, then you should provide the complete file name and size.
One of the Avast team might respond here and wish you to send it in for examination, but you can send it to support@asw.cz with an explanation. They might not respond as quickly as we here at the forum, but they need to know so they can determine if a fix is needed.
Good luck
Techie