Jacob Metcalfe
Thanks for the quick reply,
51566 does seem very similar. I do not experience the issue from bug 9810 in any of the compilers where I have managed to reproduce the bug - from a quick look it looks somewhat different - and unfortunately changes to access_specifier.hpp don't solve the issue (changing the inheritance modifier or access modifiers in the derived class also does not seem to help).
I experimented with a few changes but the only case that got rid of the error was the obvious change of making node_type public in index_base.hpp.
I'm sorry this didn't work. Given that the error seems somewhat spurious (i.e. hard to reproduce) I'm reluctant to apply the wholesale workaround of changing node_type to public in index_base. If you can live with applying this patch locally I'd rather leave it like that. Joaquín M López Muñoz Telefónica Digital