what is the "VSL interpreter"?

Hello,

I'm debugging a C++ application using DDD
on the top of GDB.

In a certain point I get a very unespected result from my code;
carefully looking at what's happening (step, step, step, ...),
I dive into the implementation of the <boost/function.hpp>
header (which I use)
http://www.boost.org/doc/libs/1_36_0/doc/html/function.html
and I get the terrifying message from the DDD interface:

"The VSL interpreted failed:
[ ... the file and line number where things go wrong ...]
infinite recursion"

Well, I would like to know if this is a warning that
I can ignore (something like "switch feature xy off and
continue debugging peacefully"), or if the machine
is trying to say something to me.

The problem is that I have no idea of what VSL is.
My usual "learning techniques" didn't produce anything
interesting:
CTRL+F inside the DDD manual, Google queries, en.wikipedia...

Regards,
Giovanni Gh.