NoClassDefFoundError in max for live

I’m working on a max for live device for a client. On my computer everything works fine, but on the clients computer I get a runtime error:
It inits the object but when a method is called I get: NoClassDefFoundError.

[attachment=218098,5203]

import com.cycling74.max.*;
import com.cycling74.msp.*;

public class BufferTool extends MaxObject {

	String buffer = null;
	String Temp = null;

	BufferTool(Atom[] buff) {
		declareInlets(new int[] { DataTypes.ALL });
		declareOutlets(new int[] { DataTypes.ALL });
		createInfoOutlet(false);

		if (buff.length > 0)
			set(buff[0].toString());
	}

	public void set(String name) {
		buffer = name;
	}

	public void setTemp(String Temp) {
		this.Temp = Temp;
	}

	public void combine() {

		MaxSystem.deferLow(new Executable() {
			@Override
			public void execute() {

				...

			}
		});
	}

}

The java.class file is in the max search path and the max.java.config has been edited.

Any help will be much appreciated!!