Complete abstinence from intercourse from the screening visit, throughout the trial and for 7 (~5 half-lives of GSK256066) days after the completion of the trial; or Male partner was sterile prior to the female subject's entry into the study, or Implants of levonorgestrel inserted for at least 1 month prior to the study medication administration but not beyond the third successive year following insertion; or Injectable progestogen administered for at least 1 month prior to the study medication administration and administered for 1 month following study completion; or Oral contraceptive (combined or progestogen only) administered for a least one monthly cycle prior to study medication administration; or The contraceptive transdermal patch, Ortho Evra (if the subject is less than 89kg); or Double-barrier method - spermicide plus a mechanical barrier (e.g., spermicide plus a male condom or a spermicide and female diaphragm.