An expression contained a forward reference to a location that was later determined to be of FAR distance. When forward references are used, the assembler makes default assumptions about the eventual definition of undefined labels used in the expression; such definitions are never assumed to be in a different segment. Use of such an expression can cause differences between the code generated on the first and second passes of the assembler.
Recovery: Qualify the expression with a distance override (FAR, FAR16, or FAR32) or segment override (:) operator.