Tha problem of Keil is that it has not true header description (like this): http://www.keil.com/dd/chip/3986.htm 

There it was told to use "at89c51xd2.h" for AT89C51RE2, but I can't find there BDRCON_1 register (for ex, 0xBCh in PDF, snd uart) and some other. Anyway, I have most newest v4.22 of