In performing tests with the CRTM, work at the Cooperative Institute for Research of the Atmosphere (CIRA) found that forward radiance calculations have significant errors for wavelengths that include a solar reflected component, such as 3.9 μm and below. Brightness temperature errors were as large as 50 K for optically thick ice clouds. Satellite-observed radiances in the near infrared (e.g., 3.9 μm) are very sensitive to hydrometeor particle size, so CRTM accuracy for these clouds is critical for diagnosing possible problems with model microphysics schemes. In collaboration with the CRTM team at the JCSDA, a study is currently underway to identify the source of the error in the CRTM and to suggest a fix. This presentation will provide details of the ongoing work and present the most recent findings.