I am using MM 2007. I made a typo in the investment name and assigned it the correct stock symbol. Now I can't change the investment to the correct name, because the program says that it is already assigned to the correct stock symbol.
How to change this investment name?
You have the correct symbol, but the wrong name. Right-click any reference to that stock, and choose InvestmentDetails or GoToInvestment->Details. There you will see a Rename button in the upper right.