Why are you running a boot-time scan as it is a specialist scan, used when an infection can't be dealt with in normal mode ?
When selecting a boot-time scan you can change the options, if I ever run one (rare as hens teeth), then I wouldn't scan archives as:
1. this is a pointless exercise as they are inert until unpacked and any executable run; before that happens the file system shield would scan the extracted files (depending on type) and scan executables before they can run.
2. decompression bombs are archives, so by not scanning them you are less likely to encounter this notice.
3. you can also pre-select the actions to take in the scan, see image (this is from avast 7 but is essentially the same in avast 6). Yours I would guess is set to Ask, you can choose Move to Chest or No Action (you should get a list at the end of the scan or check the boot-time log file). Under no circumstances should you choose delete, you have no other options.