What caused this error?

[gxygogogo]

In [4]: registrar = registration.Valis(slide_src_dir,
...: results_dst_dir,
...: micro_rigid_registrar_cls = micro_rigid_registrar.MicroRigidRegistrar,
...: #max_processed_image_dim_px = 2000,
...: #max_non_rigid_registration_dim_px = 1500,
...: norm_method = 'img_stats')
...:
/usr/local/src/valis/valtils.py:29: UserWarning: Can't find slide file associated with Micro-registration
warnings.warn(warning_msg, warning_type)