Many of us assume that communication with our children is about what we say and how we say it and while this IS important, it is not all there is to good communication. In fact, it might not be what you are saying but WHEN you are trying to say it. There really is a right and wrong time to talk about things. Waiting for the right time might make it more likely that your child will hear what you have to say and good communication will occur.
There is definitely something to be said for tact and timing in parental conversations. Just as it right before a big presentation at work is not the time for you to have your best friend tell you your hair looks terrible or you have an annoying way of speaking when you get nervous, there are likely times when it is better to talk about certain things with your children. Finding the right time and taking into consideration the mood of the child and the situation can make the difference between successful communication and an unsuccessful chat.
I am not advocating procrastination or putting off important conversations, but there are times when children are more open and susceptible to listening and communicating. For example, trying to talk about future college plans while a teenager is cramming for an important final or trying to get ready to go to a dance is probably not going to work. Having a leisurely chat about options over a breakfast out or while driving to the mall might make better sense.
It may be that it is not that you and your child cannot talk to each other or communicate, it may just be that you are choosing the wrong times to bring things up. Consider timing and you may find your parent-child communication improves.