Which operating system are you using?
Which camera are the camera raw files from?
Since pse 11 can only use up to camera raw 7.4, look at this chart and see if your camera requires a newer version of camera raw.
Camera Raw plug-in | Supported cameras
If your camera requires a newer camera raw plugin than 7.4, then you can probably use the adobe dng converter to convert the files to dng copies, which pse 11 should then open.