OK, so now you are root with opensh. The problem seems to be that the script can't find some executables, in this case modprobe (which is used to insert modules in the kernel - the ext2 file system module, here, since N9 doesn't use that by default).
To start, the error you currently have comes from the qmount script. It says it can't find modprobe. By default, Linux systems store user-and-root-executable programs in the /usr/bin directory and only-root-executables in /sbin. Therefore, it is possible that since these scripts are a direct port from the N900, modprobe was in /usr/src on the N900, but it's in /sbin on the N9.
So, what you have to do is edit at least the closechroot, qchroot, qmount, qumount, synchroot and debian scripts and correct every path of a program that gives you an error when trying to chroot.
Here it clearly says modprobe, so, in the file qmount, replace modprobe with /sbin/modprobe. You could also look in /usr/sbin, some important programs are there instead.
And so on and so forth until you have corrected all the paths, which is when you'll have a fully functional chroot. Sorry for the lenghty post, I hope it helps.