Outlook button "spam" greyed out for second account

Dear,

  • Outlook 2010 with two accounts (both same domain)
  • avast progr version 8.0.1490 / virus definitions version 131128-1 / # of definitions 6.442.133 = most recent version and definitions
  • After an avast update yesterday, the avast spam button is greyed out in one of the two accounts

How can I reactivate this button?

Many thanks in advance!

Claudio