Update section of upgrade fails

I was upgrading to wordpress 2.7 and i backed up, updated the files on the server then went to upgrade.php
It failed. So I reuploaded the old files. Blog was back to normal and tried the upgrade again. Again upgrade failed. So this time I deleted everything on the server, rolled back to the orginal state, confirmed it and ran the update again. Again it failed

Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.

What do I do?