You will save a lot of time if you provide as much detailed information as possible. First, there is no way to continue without restarting so you must fix this.
Second. There is an incompatibility with the System, Screen Saver software, or other "extensions" depending on the System version you are running. The only way to help you is for you to give a detailed list of items installed running in your Classic System and what ScreenSaver you are trying to run. The most likely answer, and one you don't want to hear is that the System you want to run is incompatible with the Screen Saver which most likely requires an older or newer System version. Alternatively you may be able to find a more compatible version of the screen saver software.