Cannot open assigned task in Outlook 2003

[rgsiii]

I am using Outlook 2003 SP2 on a 2000 Professional PC. When a
co-worker creates and assigns me a task, it comes into my Inbox and I
can see it in my preview pane, but I cannot open it when I double-click
it and I cannot accept or decline it thru the preview pane. My
co-worker has Outlook 2002 and has no problem opening and accepting
tasks from me. By the way....when I attempt to open it, absolutely
nothing happens that I can see....no error, no change of screens.

Thanks,
Robert Shurtleff