classnotfoundexception when attempting to debug java project in eclipse

I have a java project in eclipse that I exported and then re-imported. I'm able to build it without any errors and I verified that the .class files get generated on the file system. But when I try to debug it, I get a classnotfound exception:

 

New_configuration (1) [Java Application]	
	pikefin.PopulateSpreadsheet at localhost:39823	
		Thread [main] (Suspended (exception ClassNotFoundException))	
			URLClassLoader$1.run() line: 217	
			AccessController.doPrivileged(PrivilegedExceptionAction<T>, AccessControlContext) line: not available [native method]	
			Launcher$AppClassLoader(URLClassLoader).findClass(String) line: 205	
			Launcher$AppClassLoader(ClassLoader).loadClass(String, boolean) line: 319	
			Launcher$AppClassLoader.loadClass(String, boolean) line: 294	
			Launcher$AppClassLoader(ClassLoader).loadClass(String) line: 264	
			Launcher$AppClassLoader(ClassLoader).loadClassInternal(String) line: 332	
			AltRegistry.<init>(AltRegistry) line: 118	
			AltRegistry.<init>() line: 100	
			Service.<clinit>() line: 555	
			PopulateSpreadsheet.<init>(String) line: 87	
			PopulateSpreadsheet.main(String[]) line: 243	
	/usr/lib/jvm/java-1.6.0-openjdk-1.6.0.0.x86_64/bin/java (Apr 19, 2011 12:24:17 PM)

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I verfied that the folder with the class files is in the run/debug configuration classpath:


Screenshot-Edit-Configuration-.png