Jesse Perring and reaperman have a number of threads that have helped many resolve their Maestro problems.
LOL was running fine for me up until a couple days ago. Though my setup hadn't changed, Maestro was suddenly crashing on me. After trying many of the normal things (driver updates, firewall, antivirus, reinstall, etc.), I did some investigating and found that I could log in with a new account but not my normal account. Since I had recently added a large number of friends, I suspected that was it. It has now been confirmed by Riot:
Their fix for me is to use my "new" account. Unfortunately, this means that I won't be getting the XP bonus and IP bonus that I had paid for and earned. But perhaps this helps some of the frustrated users having issues with Maestro.