The erasing process of stripe domains in (111)-oriented garnet bubble films was investigated experimentally in the presence of both an in-plane field Hin and a static bias field Hb. As Hb was kept constant and Hin was raised, the stripe domain erasing field Hs* and the bubble domain erasing field Hk* were measured as functions of the azimuthal angle β of the in-plane field. Taking the cubic magnetocrystalline anisotropy into account, we established a theory of stability of stripe domains subjected to both an inplane field and a static bias filed. The main features of the experimental results can be explained qualitatively by this theory. The angle at which both white and black domains are erased at the same time was obtained as βn=1/3(2nπ±arc cos│3/(21/2)(MsHb)/K1│)(n=0,±1,±2,…) which is in reasonable agreement with the experiments.