I recently stumbled across an issue with my ConTeXt set up, while looking at a question about TikZ and ConTeXt. While ConTeXt Mark II was fine, I got the rather cryptic error:

mtxrun          | forcing cache reload
resolvers       | resolving | configuration files already identified
resolvers       | resolving | skipping configuration file
'selfautoparent:/texmfcnf.lua' (no content)
resolvers       | resolving | no texmf paths are defined (using TEXMF)
resolvers       | resolving |
mtxrun          | the resolver databases are not present or outdated
resolvers       | resolving | using suffix based filetype 'lua'
resolvers       | resolving | using suffix based filetype 'lua'
resolvers       | resolving | remembered file 'mtx-context.lua'
resolvers       | resolving | using suffix based filetype 'lua'
mtxrun          | unknown script 'context.lua' or 'mtx-context.lua'

when trying to run ConTeXt Mark IV. It seems that this because I installed MacTeX 2011 during pre-testing. A quick e-mail to the ConTeXt mailing list pointed to the file /usr/local/texlive/2011/texmfcnf.lua, which for me read

-- (Public domain.)
-- This texmfcnf.lua file should exist only if you have personal changes
-- from the distributed file; for example, if TEXMFVAR was changed in
-- the installer.
--
return { TEXMFCACHE = '~/Library/texlive/2011/texmf-var' }

It seems that this is defective, as replacing the content with

return {
  content = {
    variables = {
      TEXMFHOME = "~/Library/texmf",
      TEXMFVAR = "~/Library/texlive/2011/texmf-var",
      TEXMFCONFIG = "~/Library/texlive/2011/texmf-config",
    },
  },
}

(as suggested by Mojca Miklavec) sorted the issue straight away.