Error clonning ublas in modular-boost.

Hello all,

I've created a Windows based virtual machine. I would like to clone
modular-boost as shown in the instruccions of the wiki, but it is not
possible to checkout ublas:

C:\Users\qduran\development\modular-boost>"c:\Program Files (x86)\Git\
bin/git" submodule update --init --recursive
fatal: reference is not a tree: 6ef6cd8ba14d5a5e109324c5c781a2a407d8767f

The commit 6ef6cd8ba14d5a5e109324c5c781a2a407d8767f is only present in
boostorg/ublas master branch. I remembed that this issue also occured
previously.

Thanks and Best Regards,
Joaquim Duran