From Columbia University FAQ's
http://www.columbia.edu/cu/biology/ug/advice/faqs/gs.html
Why do I have to take chemistry before biology?
A3: There is a big difference between most college science courses and most high school science courses. In high school, you are usually expected to memorize the basic facts and principles. In college, you are expected to learn the facts in much more detail and you are also expected to understand the principles in much greater depth (this is usually the hard part). This means (in practical terms) that on exams you are asked to apply the principles that you have learned to solve problems and to explain totally new situations. This is just as true of biology as it is of physics and chemistry -- college biology is an experimental science, not a descriptive science. If you jump straight into Biology C2005/F2401 without a year of college chemistry to help you "rev up" you are likely to find the biology overwhelming.
It also pays to take chemistry first for another reason. Most students who take biology need to take chemistry (eventually). If you are going to take chemistry anyway, you might as well take it first so that the molecular parts of bio will make more sense. Biologists use chemistry as language, the way physicists use math. You can explain physics without math, but it takes a lot longer and the explanations are not as satisfying, or you have to teach the math as you go along. So it is simpler to just do the math first and the physics after. Similarly, it makes more sense to do the chemistry first and the biology second.
You also said that in chemistry you had a problem with something. Can you elaborate that? Perhaps lacking a strong foundation before starting general chemistry?