Looked for this in JIRA for a bit and found https://issues.jenkins-ci.org/browse/JENKINS-16862 which is close to the issue I'm seeing, but not sure if really a dupe.

After upgrade to 1.502, hudson.tasks.Mailer.UserProperty is unresolvable in a groovy script which emails the user (LDAP) who kicked off the job.

Stack dump is:

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
/mnt/cns/DeviceMgmt/jenkins/scripts/JenkinsEmailer.groovy: 50: unable to resolve class hudson.tasks.Mailer.UserProperty
@ line 50, column 37.
if (userProp instanceof hudson.tasks.Mailer.UserProperty)
^

1 error

at org.codehaus.groovy.control.ErrorCollector.failIfErrors(ErrorCollector.java:302)
at org.codehaus.groovy.control.CompilationUnit.applyToSourceUnits(CompilationUnit.java:858)
at org.codehaus.groovy.control.CompilationUnit.doPhaseOperation(CompilationUnit.java:548)
at org.codehaus.groovy.control.CompilationUnit.compile(CompilationUnit.java:497)
at groovy.lang.GroovyClassLoader.doParseClass(GroovyClassLoader.java:306)
at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:283)
at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:267)
at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:197)
at groovy.lang.GroovyClassLoader$parseClass.call(Unknown Source)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:42)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:108)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)
at Script1.run(Script1.groovy:11)
at groovy.lang.GroovyShell.evaluate(GroovyShell.java:580)
at groovy.lang.GroovyShell.evaluate(GroovyShell.java:618)
at groovy.lang.GroovyShell.evaluate(GroovyShell.java:589)
at groovy.lang.Script.evaluate(Script.java:208)
at groovy.lang.Script$evaluate.callCurrent(Unknown Source)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallCurrent(CallSiteArray.java:46)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:133)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:141)
at Script1.run(Script1.groovy:14)
at groovy.lang.GroovyShell.evaluate(GroovyShell.java:580)
at groovy.lang.GroovyShell.evaluate(GroovyShell.java:618)
at groovy.lang.GroovyShell.evaluate(GroovyShell.java:589)
at org.jvnet.hudson.plugins.groovypostbuild.GroovyPostbuildRecorder.perform(GroovyPostbuildRecorder.java:276)
at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:19)
at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:814)
at hudson.model.AbstractBuild$AbstractBuildExecution.performAllBuildSteps(AbstractBuild.java:786)
at hudson.model.Build$BuildExecution.post2(Build.java:183)
at hudson.model.AbstractBuild$AbstractBuildExecution.post(AbstractBuild.java:733)
at hudson.model.Run.execute(Run.java:1593)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:237)