Are you sure that your card is in the list of supported hardware? For example, I cannot see something like "AMD Mobility Radeon HD 6400M Series" in Release notes for 14.4 Windows driver. But in Release notes for beta-driver it is written that AMD Mobility Radeon™ HD 6000M Series is supported. May be, you should install this beta-driver.
If this doesn't help, specify your operating system, please.