  We consider anomaly cancelations in Type IIB orientifolds on T^4/Z_N with
quantized NS-NS sector background B-flux. For a rank b B-flux on T^4 (b is
always even) and when N is even, the cancelation requires a 2^{b/2}
multiplicity of states in the 59-open string sector. We identify the twisted
sector R-R scalars and tensor multiplets which are involved in the
Green-Schwarz mechanism. We give more details of the construction of these
models and argue that consistency with the 2^{b/2} multiplicity of 59-sector
states requires a modification of the relation between the open string 1-loop
channel modulus and the closed string tree channel modulus in the 59-cylinder
amplitudes.
