Grails - java.lang.NoClassDefFoundError: _PluginDependencies_groovy$_run_closure1

wish helps you You do not need Groovy or Grails installed on the web server, you just need to deploy the war. The war contains the groovy-all jar and all Grails jars.
The problem here is that somehow the compiled classes from STS are making it into your war. It looks like STS is using Groovy 1.8 but you're using 1.3.x which uses Groovy 1.7 which doesn't have the BytecodeInterface8 class.

I wish this help you Running application without forking fixed the problem.
Simply add this line to BuildConfig.groovy

grails.project.fork.run=false

I wish did fix the issue. You miss the spring-mock-.jar in your classpath. Add it and the error should go away.
if you are using maven add the following dependency to your pom.xml:

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-mock</artifactId>
    <version>2.0.8</version>
</dependency>