Hi Andy,
I don't exactly know what you mean by move the start menu, but I can imagine what happens.
The Windows installer probably tries to repair something that it recognizes to be broken because a file doesn't appear where it expects it to be. You could try to uninstall 3DWatch, move whatever you want and reinstall 3DWatch.
There is also a key somewhere in the registry that prevents the Windows installer from doing this. Please have a look in the corresponding newsgroups an let us know if you find a solution.
Have nice day!
Thomas