Advice needed - Avast update not working?

I installed Avast on Vista HE. After restarting computer, it started work, generated icons etc. But Windows Security Center gives worning that Virus protection does not work - antivitus reports that it might out of date. I klicking update now, but no effort happends - the warning still keep showing. Can anybody advice, how get it to proper mode? Has Windows Firewall blocking this…
Thanks in advance.

Is your computer time/date/mnd/year correct?..if not adjust and restart

Time and date are ok. Restarted and WSC warning does not apply anymore. Avast ball is circulating correctly. I quess it helped. Thanks!