You should pause the standard shield when doing another security scan. This not only avoids potential conflict but also stops duplication of scanning and will speed up the scan duration.
What I believe is happening is as adaware unpacks files avast is detecting signatures, because of what avast an on-access scanner it will intercept any file opened or unpacked for scanning and scan it before releasing it for the other process.
adaware also unpacks its signature files and avast can see and detect these.
What would have been helpful would have been the malware name, the infected file name, where was it found e.g. (malware name, C:\windows\system32\infected-file-name.xxx) ? Check the avast! Log Viewer (right click the avast icon), Warning section, this contains information on all avast detections.
