I encounter the same thing in interviews, MerryRaven.
Sometimes a candidate with a great resume has the personality of wallpaper paste. You know they can do the job, but in terms of customer service and working with the rest of the staff, you need to hire someone with some personality. I feel bad, and I do everything I can to open someone up, but sometimes gettimg more than a one word answer is like getting blood from a stone.
Last year we interviewed this great girl. Super resume, really good experience, she'd worked at some really good companies but she was such a little mouse in her interview. She was so nervous she could hardly form sentances. We did hire her because she was really well qualified, but we had bets going on how long it would be before she ended up in the bathroom crying.
It took her a few weeks to get comfortable, but she did open up eventually (and I think made it through the year without crying in the bathroom...or maybe she did and no one ever told me!)