3.1.2 is not yet available for download, we are planning to release it soon - it should be available within a couple of days.

is this available for download? or ETA on when it will be available for download?

The 2 variables I am using in plugin configuration are ${bamboo.buildNumber}_${bamboo.custom.brmp.version}
I dont have any plan variables defined.

This problem is about to be fixed in Bamboo 3.1.1 that should be released soon.
Could you confirm - are you using global or plan variables in plugin configuration?

Still get the same error with version 2.0.4

Let me know if you need me to upload any logs.

Build Assay Design - Sprint 4 : PostChainAction
(java.lang.NullPointerException : )

Occurred: 20 May 2011, 9:49:18 AM
java.lang.NullPointerException
at java.util.HashMap.<init>(Unknown Source)
at com.google.common.collect.Maps.newHashMap(Maps.java:136)
at com.atlassian.bamboo.variable.CustomVariableContextImpl.filterVariableContextByName(CustomVariableContextImpl.java:269)
at com.atlassian.bamboo.variable.CustomVariableContextImpl.substituteBambooVariables(CustomVariableContextImpl.java:159)
at com.atlassian.bamboo.variable.CustomVariableContextImpl.substituteString(CustomVariableContextImpl.java:129)
at com.atlassian.bamboo.build.VariableSubstitutionBeanImpl.substituteBambooVariables(VariableSubstitutionBeanImpl.java:51)
at com.atlassian.bamboo.build.VariableSubstitutionBeanImpl.substituteBambooVariables(VariableSubstitutionBeanImpl.java:36)
at com.sysbliss.bamboo.plugins.brmp.action.postrunners.TaggerRunner.runTagger(TaggerRunner.java:74)
at com.atlassian.bamboo.plugins.brmp.action.BRMPChainCompleteAction.execute(BRMPChainCompleteAction.java:61)
at com.atlassian.bamboo.chains.ChainPluginSupportImpl.chainCompleted(ChainPluginSupportImpl.java:94)
at com.atlassian.bamboo.chains.ChainExecutionManagerImpl.finaliseChainStateIfChainExecutionHasCompleted(ChainExecutionManagerImpl.java:531)
at com.atlassian.bamboo.chains.ChainExecutionManagerImpl.access$600(ChainExecutionManagerImpl.java:50)
at com.atlassian.bamboo.chains.ChainExecutionManagerImpl$1.run(ChainExecutionManagerImpl.java:282)
at com.atlassian.util.concurrent.ManagedLocks$ManagedLockImpl.withLock(ManagedLocks.java:333)
at com.atlassian.bamboo.chains.ChainExecutionManagerImpl.execute(ChainExecutionManagerImpl.java:241)
at com.atlassian.bamboo.chains.ChainExecutionManagerImpl.access$1000(ChainExecutionManagerImpl.java:50)
at com.atlassian.bamboo.chains.ChainExecutionManagerImpl$2.run(ChainExecutionManagerImpl.java:328)
at com.atlassian.util.concurrent.ManagedLocks$ManagedLockImpl.withLock(ManagedLocks.java:333)
at com.atlassian.bamboo.chains.ChainExecutionManagerImpl.handleEvent(ChainExecutionManagerImpl.java:308)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:304)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:182)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
at org.springframework.orm.hibernate.HibernateInterceptor.invoke(HibernateInterceptor.java:117)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
at $Proxy49.handleEvent(Unknown Source)
at com.atlassian.event.legacy.LegacyListenerHandler$LegacyListenerInvoker.invoke(LegacyListenerHandler.java:55)
at com.atlassian.event.internal.AsynchronousAbleEventDispatcher$2.run(AsynchronousAbleEventDispatcher.java:60)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at com.atlassian.bamboo.build.pipeline.concurrent.NamedThreadFactory$2.run(NamedThreadFactory.java:50)
at java.lang.Thread.run(Unknown Source)

Can you try version 2.0.4 ?