Spark ClassNotFoundException running the master

I have downloaded and built Spark 0.80 using sbt/sbt assembly. It was successful. However when running ./bin/start-master.sh the following error is seen in the log file

Spark Command: /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home/bin/java -cp :/shared/spark-0.8.0-incubating-bin-hadoop1/conf:/shared/spark-0.8.0-incubating-bin-hadoop1/assembly/target/scala-2.9.3/spark-assembly-0.8.0-incubating-hadoop1.0.4.jar
/shared/spark-0.8.0-incubating-bin-hadoop1/assembly/target/scala-2.9.3/spark-assembly_2.9.3-0.8.0-incubating-hadoop1.0.4.jar -Djava.library.path= -Xms512m -Xmx512m org.apache.spark.deploy.master.Master --ip mellyrn.local --port 7077 --webui-port 8080

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/spark/deploy/master/Master
Caused by: java.lang.ClassNotFoundException: org.apache.spark.deploy.master.Master
        at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:247)

Update: after doing sbt clean (per suggestion below) it is running: see screenshot.