I had/have exactly same problem http://forums.avg.com/ww-en/avg-forums?sec=thread&act=show&id=188280. I have a Paid For AVG 2012 (note 12 not 13) and the problem I believe has only started recently. Further, I do not believe I was asked to install the Toolbar and wonder whether was installed covertly with one of the recent updates. I have now both changed the file to read only AND uninstalled the Toolbar that I didnt know I had. This is only a recent problem I believe,well for me anyway, as would have noticed. I couldnt believe my HD was so full as thought I had at least 25% space but looked yesterday was 3%. I infact delete another large file I had to free up space, but this was now unnecessary as I, for a reason, found this large file (I believe was 10GB ++) .
It is NOT at all good that AVG should not have explained this or dealt with it and I for one will be very very careful in future and may well not renew with AVG next year and try another AV. If AVG start messing around and covertly installing toolbars that dont work and then failing to provide fixes then they will lose their loyal customers quicker than they think. Maybe AVG is too big now and does not care anymore?. Lets show them they are not and will lose out with sloppy work.