First,
First, have you tried installing the Stand-Alone Addon Manager ? This is always the very latest version, without the need to download the whole Zurich or O'Hare installers again.
Also, the previous poster said the startup problem was caused by FSUIPC and was solved by going to the previous version. Maybe there is a problem with the latest FSUIPC version, could you please set it to <Disabled>True</Disabled> in the DLL.XML and see if it works now ?
The same might be worth trying with every other addon module. By disabling each one (one by one, launching FSX each time), one can easily identify possible conflicts.