Don’t know. I’m running 0.3.5 on FreePBX 2.7 on Asterisk 188.8.131.52 with no issues. Did you apply any of the patches to customcontexts/functions.inc.php? Have you applied all updates for 2.7 to FreePBX?
You might try uninstalling custom-contexts and re-installing. I’ve got about 5 different custom-contexts and have not had that issue. I’ve played with FreePBX 2.8Beta on a lab box and got similar results to yours on that version because Custom-Contexts is totally incompatible with 2.8, but I don’t know what is causing your error.