Aloha P,
Shot in the dark here (and I hope I am wrong) but it sounds to me that Cubase 4
won’t run/install with OS 10.9 because It’s too old. (or the OS is too new).
I have not read anywhere that C5 runs with 10.9 so that bodes well that C4 also will not.
You may have to get a newer version of Cubase or downgrade your OS.
Also, IIRC Isn’t C4 for the Mac a PPC app? If so there is no more ‘Rosetta’ in the OS to translate to Intel.
Perhaps someone else in the forum will have another approach.
Good Luck!
{‘-’}