Sounds like nutch does not found your plugins. A stacktrace from your exception could help.
Please verify your nutch-default.xml at the property
<property> <name>plugin.folders</name> <value>plugin</value> <description>Directories where nutch plugins are located. Each element may be a relative or absolute path. If absolute, it is usedas is. If relative, it is searched for on the classpath.</ description>
</property> Marko
