diff --git a/datastore_server/source/java/ch/systemsx/cisd/etlserver/registrator/api/v2/impl/DataSet.java b/datastore_server/source/java/ch/systemsx/cisd/etlserver/registrator/api/v2/impl/DataSet.java
index 622cfff0f65590e0606591575b742fbc01f2e758..89be0aa307e7f29e670f0c46ace623d80bab75ea 100644
--- a/datastore_server/source/java/ch/systemsx/cisd/etlserver/registrator/api/v2/impl/DataSet.java
+++ b/datastore_server/source/java/ch/systemsx/cisd/etlserver/registrator/api/v2/impl/DataSet.java
@@ -97,12 +97,12 @@ public class DataSet<T extends DataSetInformation> extends AbstractDataSetImmuta
             if (contents.length > 1)
             {
                 throw new IllegalArgumentException(
-                        "Data set is ambiguous -- there are more than one potential candidates:"
+                        "Data set is ambiguous -- there are more than one potential candidates. transaction.moveFile() might have been called several times:"
                                 + Arrays.toString(contents));
             }
             if (contents.length < 1)
             {
-                throw new IllegalArgumentException("Data set is empty: "
+                throw new IllegalArgumentException("Data set is empty. transaction.moveFile() might have been ommitted: "
                         + registrationDetails.getDataSetInformation());
             }
             return contents[0];