Interviews for contract vacancies are different to permanent ones.
Contract Interviews
A contractor is often hired purely based on their skills and abilities to the do the job. A manager with a deadline to meet will need to find someone with the right skills. However you still need to convince them that you are honest, trustworthy, punctual, a team player and dedicated to getting the job finished on time.
Hopefully you now have the perfect CV. Most of the hard work is done. The employer knows they want your skills and have invited you for an interview. It will often be a fairly short interview and will be to discuss your skills. There may be one technical person and one managerial person. Make sure you know your CV inside out and can discuss how you can demonstrate your skills. If one of the interviewers makes a glaring technical error, politely pick this up. They may be trying to catch you out.
Permanent Interviews
For a permanent position the employer needs to be doubly sure that you are right for the job. A contractor may only be at a company for a short term basis whereas the permanent role could be for your whole career. You have to come across as professional, intelligent and trustworthy as well as convincing the employer that you can do the job. Once you have got over the initial euphoria of succeeding in reaching the first interview stage you must make time to prepare fully.
You can't predict what questions will be asked or at what level the interview will be conducted so preparation is vital. The interviewer will be trying to find out: