Fulvio wrote:C:\Documents and Settings\<Your Windows Username>\Application Data\Mozilla\SeaMonkey\profiles\xxxxxxxx.default
Is the profile folder which Dave referred to. You want to remove, first, it before reinstalling SM2 because its presence is preventing the launching of the Migration Assistant.
Then, uninstall SM1.1.18, the program, in Program Files and delete any files/folder which were not removed. You don't have to remove its profile folder.
It isn't essential to uninstall the SeaMonkey 1.x program files before installing SM 2.x, although you can do so if you wish.
Then reinstall SM2, and you should be asked if you want to use the Migration Assistant.
If you reinstall SM2 first, you will be back to square one.
Fulvio is quite correct, remove the SM 2.x profile before reinstalling SM 2.x!