Bonjour MatMat!
Are you sure the dialog box that appear after you click the red box says the VPS is already updated? Please checkit out again.
Also please check:
1. your firewall settings: you know how it works, you must allow the proper modules to access internet - I remember at least two of them, ashupd.exe and setup.ovr
2. also if above don't work there's a workaround you may try: uncheck the autoupdate option and try to update signatures manually, if it works all you need to do is tell avast! to wait some time after you logon so proper access to the net can be established. To do this please refer to the topic "undestanding avast4.ini file" or please do a forum search for the delay feature that lets avast! wait xx seconds until it try to autoupdate.
Hope it works, au revoir :-D