How are you trying to split the clip? There are a couple of ways to do it depending on which software you're using.
Speaking of which, if you would include some more info in your post like which version of Cakewalk's software you are using, your operating system and whether it's 32- or 64-bit and your audio interface/sound card, or better yet, permanently attach it in your signature, that will help us help you better and we won't have to ask what software, OS, etc. you're using every time you post a question.
With that info, someone will be able to help, I'm sure.