As is the case with many interview questions, the interviewer is looking for multiple items in your response to this question. S/he wants to learn things about you like motivation, honesty, and loyalty. This question should be answered in a way that spends about 20% of your time on what you actually dislike about your current position and the remainder of the time talking about why the strengths you have will make you a great candidate for the job for which you’re interviewing. A good answer might be something like,
I really do enjoy nearly every aspect of my current job. Because the majority of my product line so simple, however, I sometimes wish for more complex products that require in depth discussion and explaination. I have a handful of customers that have purchased our high-end solutions and I enjoy, and excel at, the consultative relationship I have with those companies. I love the challenge of being able to think through a complex problem with a client and working with him/her to develop a solution that meets the needs of his/her company and its customers.
If you find this site helpful, please send a link to your career services department so your fellow alumni know about PharmBoard too! I've already written the message for you. :)