yeah, that is serious... the tug daemon (which handles all the teleworker or call recording sets) has crashed.
A core file is the file the operating system creates to aid developers in debugging. It's a memory snapshot of the entire process that crashed.
The email doesn't contain the core file itself, that's too big, it only contains a "backtrace" file which is really really useful for product support and developers as it pinpoints exactly in the code where the crash occured.
Contact product support (or post the backtrace here, I'm curious).
