We are using Outlook 2010 with Exchange 2010 on Widows7 and Windows SBS2011 respectively. All worked fine until we installed Eset Antivirus 5 on every client machine. When I send a task to a user they can't accept it anymore becasue the task notification can't be opened. It says "Can't open this Item. Outlook cannot perform this type of action on this attachment". We have switched off Antivirus completely but it still gives the error. Is this an issue in the security settings of Outlook ? We have started Outlook in safe mode but that doesn't help either. To be complete I should also add that the security certifcate on Exchange has not been activated yet by our administrator but that didn't seem to be a problem before. I just mention it in case the combination of the Antivirus and the email settings would be the cause.
Thanks for your ideas, we cant find anything on the net.