nrv, please go to program settings, switch to "Report" page and enable report generation. Let all the records (even "OK files") be included. Now, run the scan again. The resulting report will be rather huge - but when it freezes (or when it seems to be frozen), you should be able to guess the current position of the scan according to the end of the report file.
(If there really is a file that makes avast! freeze, we need to identify and analyze it.)