The problem is there are a number of tools in the ultimateboot iso that can be used for good as well as evil and the problem for an AV is deciding intent.
You can pause standard shield and extract the file that is being detected (iso buster) and check that.
avast can scan iso images some other AVs can't unpack the .iso image so aren't able to do a deep scan, I don't know if this is the case with AVG.
What is the file name that is causing the alert, check the avast Log Viewer, warning section.
Assuming you can extract the file causing the alert and check that and send zipped and password protected to the email you found. I have UB CD and had this with one of the cmos tools I think had this issue but, knowing what the UB CD is about and the reason you have it after analysis you decide what you want to do.
You could also check the offending/suspect file at:
VirusTotal - Multi engine on-line virus scannerOr
Jotti - Multi engine on-line virus scanner if any other scanners here detect them it is less likely to be a false positive.
You can't do this with the file in the chest, you will need to move it out.If it is indeed a false positive, add it to the exclusions lists (Standard Shield, Customize, Advanced and Program Settings, Exclusions) and periodically check it (scan it in the chest), there should still be a copy in the chest even though you restored it to the original location. When it is no longer detected then you can also remove it from the Standard Shield and Program Settings, exclusions.
Also see
(Mini Sticky) False Positives, how to report and what to do to exclude them until the problem is corrected.
