Low Disk Space
In order to buffer content, RealTimes (RealPlayer) requires disk space on your hard drive to temporarily store information, similar to the way your web browser caches images and pages so that they display more quickly when you revisit them.
Low disk space may make it impossible to pause or cache a stream for your preferred length of time. This can occur because you have too little space on your disk to cache the current item.
Try to increase the available disk space by deleting unused or unnecessary files from your hard disk.