Problems with CI and the PHP APC extension

[eluser]tomgkelly[/eluser]
I have no APC calls at all in my CI apps. APC is definitely the direct or indirect cause of the problem. CI doesn't even get out of the chute with APC enabled.
I'm somewhat new (and enamored with) CI. I was hoping someone more adept with CI would recognize the scenario ...:

warnings that all the constants defined in constants.php have already been defined and then a fatal error that the 'controller class' is undefined.

Thanks for your input though,

Tom Kelly