I haven’t gone back to see what version of MT this starts with, but this particular setup is a Movable Type Pro 4.37 installation that was upgraded to 5.2.7. Upon publishing an entry, I observed this error screen:

An error occurred

Undefined subroutine &MT::Template::Tags::Entry::_hdlr_entries called

Through process of elimination, I traced the error to this line in a particular template:

<mt:BlogLinkedEntries field="blog_dfp_slot"></mt:BlogLinkedEntries>

This is a Field Day tag. The version installed is apparently 1.5.2 from the mt5-compat branch on Github.

I’ll update this once I dig up more information and hopefully a solution.