Thread: Main class Error

Hi, I have got a main class error, may i know what'swrong please?

// Driver for parser
package myparser;
 
import java.io.*;
import java_cup.runtime.Symbol;
import static myparser.Main.do_debug_parse;
 
 
 
 
 
//package myparser;
//import java_cup.runtime.*;
class Main {
 
  static boolean do_debug_parse = true;
 
  static public void main(String[] args) throws java.io.IOException {
      File infile = new File("C://Users//ASUS//Documents//NetBeansProjects//myparser_proj//myparser//myparser//input.txt");
     //parser parser_obj = new parser(new Yylex(fin));
      FileInputStream fin = null;
      try
      {
          fin = new FileInputStream(infile);
 
          /* create a parsing object */
          parser parser_obj = new parser(new Yylex(fin));
 
          Symbol parse_tree = null;
          if (do_debug_parse)
              parse_tree = parser_obj.debug_parse();
          else
              parse_tree = parser_obj.parse();
          System.out.println("Parse successful");
          fin.close();
      }
      catch(FileNotFoundException e)
      {
          System.out.println("File " + infile.getAbsolutePath() +
                  " could not be found on filesystem");
      }
      catch(IOException ioe)
      {
          System.out.println("Exception while reading the file" + ioe);
      }
      catch (Exception e) {
        /* do cleanup here -- possibly rethrow e */
      } finally {
	/* do close out here */
      }
  }
}

The code compiles fine but the error message is received when the code is run.
The errors are:
Exception in thread "main" java.lang.NoClassDefFoundError: myparser/Yylex (wrong name: Yylex)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java :791)
at java.security.SecureClassLoader.defineClass(Secure ClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader .java:449)
at java.net.URLClassLoader.access$100(URLClassLoader. java:71)
at java.net.URLClassLoader$1.run(URLClassLoader.java: 361)
at java.net.URLClassLoader$1.run(URLClassLoader.java: 355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.j ava:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:4 23)
at sun.misc.Launcher$AppClassLoader.loadClass(Launche r.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:3 56)
at myparser.Main.main(Main.java:27)
Java Result: 1
BUILD SUCCESSFUL (total time: 2 seconds)

No Sir there weren't any older versions in that package...

--- Update ---

But there is file denoted as Yylex.class that was generated in a different folder,I included them but still results in the same error.