#define and enum compiler error

#define USB_REQ_GET_STATUS 0
and in enum
USB_REQ_GET_STATUS = 0;

Presumably you have an enum somewhere:

enum usb_commands {
USB_REQ_GET_STATUS = 0;
 ...  more
};

This is two separate ways of defining constants. Note that you don't REALLY have a problem, since both values are the same; pick one and get rid of the other. Offhand, I'd say that the "webcam" file has no business defining primitive USB constants, and should simply be including the USB_protocol.h file to get those definitions.