This study consists of Part 1 and Part 2. Part 1 of this study is a "3+3" design to define the MTD of Oratecan in up to 60 evaluable subjects. It will be conducted in 2 parts; 1A will test the oral liquid formulation and 1B will test the oral tablet formulation of irinotecan. Part 2 will enroll an additional 10 subjects at the Part 1 MTD to further characterize the safety, tolerability, pharmacokinetics, and activity of Oratecan at that dose.