For several days, some of the bk commands have been failing on my machine with the following error message:

Missing filename ("/bin/more - \?" for help)

Today I finally took the time to reseach what was causing this.  The cause, as it turns out, was that bk was finding /bin/more as part of SUA but the argument syntax was apparently not compatible.  However, because bk found it, it tried to use it rather than fall back to it's own built-in less.exe.  I was not using SUA, so a quick uninstall had me going again.