I found this error on the wiki, on certain pages. The pages do not render, and instead provide the error message Fatal exception of type MWException.

The pages can be viewed as source, and history works. However, probably because of something in the markup, the rendering engine fails.

Pages affected by the error include:
https://wiki.dmt-nexus.me/Banisteriopsis_caapi
https://wiki.dmt-nexus.me/Peganum_harmala
https://wiki.dmt-nexus.me/Psychotria_viridis