When I launch Outlook it runs the install program each time and sometimes runs it and fails to launch. I had this same problem over a year ago and MS support spent hours repairing it and it has run fine until recently. Originally Access displayed the same behavior, but it is solid now. Secondly, if OL launches into anything except MAIL when I click on MAIL it reruns the install.
I have unistalled, run repair, pulled out my hair ... but nothing seems to help. Weirdly when Windows update runs unattended it shuts down OL and upon reboot it opens OL with no problem.