Since I started using Outlook 2010 a couple weeks ago I have been monitoring this problem but it is not going away.
(1) Start outlook.
(2) Use it....
(3) Close outlook.
(4) Attempt to start outlook again.
Result: Pop-up window saying just "cannot start Microsoft Outlook"
According to task manager there are no other instances of outlook running. I found one suggestion to try "outlook.exe /resetnavpane". But that attempt yields the same error. Before I went on to more drastic suggestions I have seen (system restore, outlook repair, etc.) I just tried restarting my computer. Then outlook started just fine. I later found that a complete restart was not needed; a logout then login would fix it as well.