We'd need to get the dump of the AvastSvc.exe process taken at the moment the scan is frozen, to be able to say what is going on.
To create it, you'd need to disable the avast! self-defense first (Settings / Troubleshooting), maybe also stop the Behavior Shield (it used to interfere with dumping our processes, as far as I remember) - and then start the scan. When it freezes, you can use the Task Manager (on Vista and higher): click on "Show processes from all users", select AvastSvc.exe, rightclick it and choose Create Dump File. After the dump is done, the window shows you the location of the dump - so you'd compress the file and upload it to
ftp://ftp.avast.com/incomingI would also ask first (in case the scanner doesn't actually freeze, but rather crashes - which may look as a freeze from the UI point of view) - do you have any recent unpXXXXXXXX files (where X are some numbers) in C:\ProgramData\AVAST Software\Avast\log, with timestamps corresponding to the "freezes"?
Thanks.