Hello, I am working on my hardware consist of EZUSB-FX2 USB2.0 controller chip.I am using Keil IDE as developement environment. I hava modified Descr.A51 file where all the informations related with USB descriptor are defined. Now the problem begins I have entered dw b404H ;; Vendor ID dw 1386H ;; Product ID in descr.A51 file. My problem is in the line one "dw b404H " during compilation it gives the error "ERROR A45-- Undefined Symbol- PASS 2" I do not know why this problem is coming. If I change the first nibble "b" with any value starting from 0 to 9, it works but it is not accepting any value starting from "a to f" Can any body tells me that what is the problem I am using compiler version C51 V6.10. Thanks Shikha