Could not find or load main class org.apache.zookeeper.server.quorum.QuorumPeerMain

The error message you mentioned, "Could not find or load main class org.apache.zookeeper.server.quorum.QuorumPeerMain," indicates that the Java Virtual Machine (JVM) is unable to find or load the main class required to start the ZooKeeper server.

To resolve this issue, you can try the following steps:

1. Check if ZooKeeper is properly installed and configured on your system. Make sure you have the necessary dependencies and environment variables set up correctly.

2. Verify that the classpath is set correctly. The classpath should include the directory where the ZooKeeper JAR file is located. You can check and adjust the classpath using the `CLASSPATH` environment variable or by using command-line options when running your Java program.

3. Ensure that you have the correct version of ZooKeeper. Double-check if the version of ZooKeeper you are trying to run is compatible with your system and any other dependencies.

4. If you are running ZooKeeper in a distributed mode, ensure that the configuration files are correctly set up, including the `zoo.cfg` file.

If none of these steps resolve the issue, please provide more details about your setup, such as the operating system, Java version, and any specific commands or steps you have taken.