grails 2.5.6 Error executing script RunApp

Question

The application is upgraded from grails 2.0.4 to 2.5.6

When running grails war or grails run-app, it fails with a message

| Environment set to development.....
| Packaging Grails application.....
| Error Error executing script RunApp: grails/plugins/Plugin 

grails compile works fine. grails clean and clean-all have no effect. Delete the scriptCache and even the whole %HOME%\.grails directory have no effect.

A new helloworld app compiles and runs just fine in the same environment after experiencing the error in the main application.

I know plugins changed. Is there something on imports or other configuration that might be impacting this?

stacktrace below

| Loading Grails 2.5.6
| Configuring classpath
| Configuring classpath.
| Environment set to development
| Environment set to development.
| Environment set to development..
| Environment set to development...
| Environment set to development....
| Environment set to development.....
| Packaging Grails application
| Packaging Grails application.
| Packaging Grails application..
| Packaging Grails application...
| Packaging Grails application....
| Packaging Grails application.....
| Error Error executing script RunApp: grails/plugins/Plugin (NOTE: Stack trace has been filtered. Use --verbose to see entire trace.)
java.lang.NoClassDefFoundError: grails/plugins/Plugin
    at _PluginDependencies$_run_closure2.doCall(_PluginDependencies.groovy:48)
    at org.codehaus.gant.GantMetaClass.invokeMethod(GantMetaClass.java:133)
    at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure16_closure18.doCall(GantBinding.groovy:185)
    at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure16_closure18.doCall(GantBinding.groovy)
    at org.codehaus.gant.GantBinding.withTargetEvent(GantBinding.groovy:90)
    at org.codehaus.gant.GantBinding.this$4$withTargetEvent(GantBinding.groovy)
    at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure16.doCall(GantBinding.groovy:185)
    at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure16.doCall(GantBinding.groovy)
    at org.codehaus.gant.GantMetaClass.invokeMethod(GantMetaClass.java:133)
    at _GrailsPackage$_run_closure2.doCall(_GrailsPackage.groovy:57)
    at org.codehaus.gant.GantMetaClass.invokeMethod(GantMetaClass.java:133)
    at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure16_closure18.doCall(GantBinding.groovy:185)
    at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure16_closure18.doCall(GantBinding.groovy)
    at org.codehaus.gant.GantBinding.withTargetEvent(GantBinding.groovy:90)
    at org.codehaus.gant.GantBinding.this$4$withTargetEvent(GantBinding.groovy)
    at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure16.doCall(GantBinding.groovy:185)
    at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure16.doCall(GantBinding.groovy)
    at org.codehaus.gant.GantMetaClass.processClosure(GantMetaClass.java:81)
    at org.codehaus.gant.GantMetaClass.processArgument(GantMetaClass.java:95)
    at org.codehaus.gant.GantMetaClass.invokeMethod(GantMetaClass.java:128)
    at RunApp$_run_closure1.doCall(RunApp.groovy:28)
    at org.codehaus.gant.GantMetaClass.invokeMethod(GantMetaClass.java:133)
    at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure16_closure18.doCall(GantBinding.groovy:185)
    at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure16_closure18.doCall(GantBinding.groovy)
    at org.codehaus.gant.GantBinding.withTargetEvent(GantBinding.groovy:90)
    at org.codehaus.gant.GantBinding.this$4$withTargetEvent(GantBinding.groovy)
    at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure16.doCall(GantBinding.groovy:185)
    at org.codehaus.gant.GantBinding$_initializeGantBinding_closure5_closure16.doCall(GantBinding.groovy)
    at gant.Gant$_dispatch_closure5.doCall(Gant.groovy:381)
    at gant.Gant$_dispatch_closure7.doCall(Gant.groovy:415)
    at gant.Gant$_dispatch_closure7.doCall(Gant.groovy)
    at gant.Gant.withBuildListeners(Gant.groovy:427)
    at gant.Gant.this$2$withBuildListeners(Gant.groovy)
    at gant.Gant.dispatch(Gant.groovy:415)
    at gant.Gant.this$2$dispatch(Gant.groovy)
    at gant.Gant.invokeMethod(Gant.groovy)
    at gant.Gant.executeTargets(Gant.groovy:591)
    at gant.Gant.executeTargets(Gant.groovy:590)
Caused by: java.lang.ClassNotFoundException: grails.plugins.Plugin
    ... 38 more
| Error Error executing script RunApp: grails/plugins/Plugin

Answer 1

grails.plugins.Plugin is not a class in Grails 2.5.6 but in grails 3 (as evidence by checking their API http://docs.grails.org/2.5.6/api/ vs http://docs.grails.org/latest/api/grails/plugins/Plugin.html).

Appears you have somehow pulled in a Grails 3 plugin into a Grails 2.5.6 project. You will have to resolve that by checking your BuildConfig.groovy and changing the version of the offending plugin(s) or removing them.