diff --git a/java/src/org/broadinstitute/sting/gatk/walkers/variantrecalibration/GenerateVariantClustersWalker.java b/java/src/org/broadinstitute/sting/gatk/walkers/variantrecalibration/GenerateVariantClustersWalker.java
index 3f9af10d8..16420b6fd 100755
--- a/java/src/org/broadinstitute/sting/gatk/walkers/variantrecalibration/GenerateVariantClustersWalker.java
+++ b/java/src/org/broadinstitute/sting/gatk/walkers/variantrecalibration/GenerateVariantClustersWalker.java
@@ -219,6 +219,7 @@ public class GenerateVariantClustersWalker extends RodWalker<ExpandingArrayList<
 
     public ExpandingArrayList<VariantDatum> reduce( final ExpandingArrayList<VariantDatum> mapValue, final ExpandingArrayList<VariantDatum> reduceSum ) {
         reduceSum.addAll( mapValue );
+
         return reduceSum;
     }
 
diff --git a/java/src/org/broadinstitute/sting/gatk/walkers/variantrecalibration/VariantDataManager.java b/java/src/org/broadinstitute/sting/gatk/walkers/variantrecalibration/VariantDataManager.java
index a670e4f12..ac60c4b07 100755
--- a/java/src/org/broadinstitute/sting/gatk/walkers/variantrecalibration/VariantDataManager.java
+++ b/java/src/org/broadinstitute/sting/gatk/walkers/variantrecalibration/VariantDataManager.java
@@ -53,7 +53,7 @@ public class VariantDataManager {
         numVariants = dataList.size();
         data = dataList.toArray( new VariantDatum[numVariants] );
         if( numVariants <= 0 ) {
-            throw new StingException( "There are zero variants with > 0 clustering weight!" );
+            throw new StingException( "There are zero variants with > 0 clustering weight! Please provide training sets using the dbsnp, hapmap, or 1kg rod bindings. Clustering weights can be specified using -weightDBSNP, -weightHapMap, and -weight1KG" );
         }
         if( _annotationKeys == null ) {
             numAnnotations = 0;