The disc can’t be burned because the disc drive is not accessible (error code 0x80020020).

You need to include more information about what your problem is, i.e. what system are your running, what application is this occurring in, what fixes you've tried, etc. The following will help you in that: Writing an effective Apple Support Communities question

Is the optical drive recognized by Disc Utility? Have you tried burning disk with another app, i.e. the Finder?