You must have caught it during deployment. I'd moved some stuff around, so after deploying the new version and before reloading the Fusebox, that error (along with a couple others) could be witnessed. The file in question (udflib_layouts.cfm) switched circuits from 'c' to 'lay' during that time, so the old cached version of the Fusebox memory structures would still have been looking for the file in the old location.

missing Fuse – You tried to include a fuse udflib_layouts.cfm in circuit c which does not exist (from fuseaction c.init).