Until the section is properly fixed, here is a temporary workaround: You can add ?tmpl=component to the end of any URL on the midi.org site to show the main component of the page in a default format without the header, footer, and margin items.
Edit to add: ?tmpl works too and is shorter to type.
Note: When I visit www.midi.org/specifications , I get the same SQL error message shown in Clemens Ladisch's and Max Dobroselsky's screenshots. I noticed that the "GROUPS" number in the error message is 1 when I am logged out and 2 when I am logged in. Perhaps the "The MIDI Association" account is part of a user group that doesn't trigger the SQL error? Try visiting the page when logged out or as a different user name.
If I visit www.midi.org/specifications?tmpl the page will display the expected items without the header, footer and right-margin tree. I wonder if the SQL error is related to one of those elements? Or at least, examining the difference between www.midi.org/specifications and www.midi.org/specifications?tmpl can probably help troubleshoot the issue.