Others have had the missing DSAPI.dll problem with built-in RealSense cameras on other models of computer such as Lenovo, so it is not just you. It tends to be associated with trying to run a calibrator program. Though the SR300 does not have a calibrator app (the R200 does). Is the calibrator you are using a program that came with your computer?
Sometimes a file may fail to be found because a Windows registry file is corrupted. Microsoft have a tool that can fix corrupted registries, and is especially useful for programs that can't be installed or uninstalled.