Some times the anti virus itself becomes a big problem when we try to remove them and install any other anti virus program other then. Same is the case with AVG Free Antivirus which does not remove completely from your computer and leave some traces in the form of registry entries which are not deleted after normal uninstall.
Some flies and registry entry created by AVG Antivirus still remains which can be removed by FREE AVG Remover Tool ( via Ghacks.net ) which is specially designed to remove all the parts of installation of AVG antivirus including registry entries and files on the disk.