diff --git a/composer.json b/composer.json
index d78be1de3..a5b5914e4 100644
--- a/composer.json
+++ b/composer.json
@@ -2,7 +2,7 @@
 	"name": "qtism/qtism",
 	"description": "OAT QTI Software Module Library",
 	"type": "library",
-	"version": "0.9.20",
+	"version": "0.9.21",
 	"authors": [
 		{
 			"name": "Open Assessment Technologies S.A.",
diff --git a/qtism/data/state/VariableDeclaration.php b/qtism/data/state/VariableDeclaration.php
index 24c3e2408..be7b1c634 100644
--- a/qtism/data/state/VariableDeclaration.php
+++ b/qtism/data/state/VariableDeclaration.php
@@ -14,7 +14,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  * 
- * Copyright (c) 2013 (original work) Open Assessment Technologies SA (under the project TAO-PRODUCT);
+ * Copyright (c) 2013-2015 (original work) Open Assessment Technologies SA (under the project TAO-PRODUCT);
  * 
  * @author Jérôme Bogaerts, <jerome@taotesting.com>
  * @license GPLv2
@@ -32,6 +32,7 @@
 use qtism\common\enums\Cardinality;
 use \SplObserver;
 use \SplObjectStorage;
+use \InvalidArgumentException;
 
 /**
  * From IMS QTI:
diff --git a/qtism/data/storage/xml/XmlCompactDocument.php b/qtism/data/storage/xml/XmlCompactDocument.php
index 21acf2e58..33891e3c9 100644
--- a/qtism/data/storage/xml/XmlCompactDocument.php
+++ b/qtism/data/storage/xml/XmlCompactDocument.php
@@ -14,7 +14,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  * 
- * Copyright (c) 2013 (original work) Open Assessment Technologies SA (under the project TAO-PRODUCT);
+ * Copyright (c) 2013-2016 (original work) Open Assessment Technologies SA (under the project TAO-PRODUCT);
  * 
  * @author Jérôme Bogaerts, <jerome@taotesting.com>
  * @license GPLv2
@@ -242,7 +242,7 @@ protected static function resolveAssessmentItemRef(ExtendedAssessmentItemRef $co
 	        $compactAssessmentItemRef->setTimeDependent($doc->getDocumentComponent()->isTimeDependent());
 	    }
 	    catch (Exception $e) {
-	        $msg = "An error occured while unreferencing file '${href}'.";
+	        $msg = "An error occured while unreferencing item reference with identifier '" . $compactAssessmentItemRef->getIdentifier() . "'.";
 	        throw new XmlStorageException($msg, $e);
 	    }
 	}
@@ -264,8 +264,8 @@ protected static function resolveAssessmentSectionRef(AssessmentSectionRef $asse
 	        return $doc->getDocumentComponent();
 	    }
 	    catch (XmlStorageException $e) {
-	        $msg = "An error occured while unreferencing file '${href}'.";
-	        throw new XmlStorageException($msg);
+            $msg = "An error occured while unreferencing section reference with identifier '" . $assessmentSectionRef->getIdentifier() . "'.";
+            throw new XmlStorageException($msg, $e);
 	    }
 	}
 	
diff --git a/test/qtism/data/storage/xml/XmlCompactAssessmentDocumentTest.php b/test/qtism/data/storage/xml/XmlCompactAssessmentDocumentTest.php
index 3f4f6820d..eadedffc2 100644
--- a/test/qtism/data/storage/xml/XmlCompactAssessmentDocumentTest.php
+++ b/test/qtism/data/storage/xml/XmlCompactAssessmentDocumentTest.php
@@ -4,6 +4,7 @@
 use qtism\data\storage\LocalFileResolver;
 use qtism\data\NavigationMode;
 use qtism\data\storage\xml\XmlDocument;
+use qtism\data\storage\xml\XmlStorageException;
 
 require_once (dirname(__FILE__) . '/../../../../QtiSmTestCase.php');
 
@@ -215,4 +216,16 @@ public function testExplodeRubricBlocks() {
 	    
 	    unlink($file);
 	}
+    
+    public function testCreateFromAssessmentTestInvalidAssessmentItemRefResolution() {
+        $this->setExpectedException(
+            '\\qtism\\data\\storage\\xml\\XmlStorageException',
+            "An error occured while unreferencing item reference with identifier 'Q01'."
+        );
+
+        $doc = new XmlDocument('2.1');
+        $file = self::samplesDir() . 'custom/tests/invalidassessmentitemref.xml';
+        $doc->load($file);
+        $compactDoc = XmlCompactDocument::createFromXmlAssessmentTestDocument($doc, new LocalFileResolver());
+    }
 }
diff --git a/test/samples/custom/tests/invalidassessmentitemref.xml b/test/samples/custom/tests/invalidassessmentitemref.xml
new file mode 100644
index 000000000..dc5cd513d
--- /dev/null
+++ b/test/samples/custom/tests/invalidassessmentitemref.xml
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<assessmentTest xmlns="http://www.imsglobal.org/xsd/imsqti_v2p1"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://www.imsglobal.org/xsd/imsqti_v2p1 http://www.imsglobal.org/xsd/qti/qtiv2p1/imsqti_v2p1.xsd"
+    identifier="invalidassessmentitemref" title="Invalid AssessmentItemRef">
+    <testPart identifier="T01" navigationMode="nonlinear" submissionMode="individual">
+        <assessmentSection identifier="S01" title="Section 01" visible="true">
+            <assessmentItemRef identifier="Q01" href="../../invalid/invalidresponseidentifier.xml"/>
+        </assessmentSection>
+    </testPart>
+</assessmentTest>
diff --git a/test/samples/invalid/invalidresponseidentifier.xml b/test/samples/invalid/invalidresponseidentifier.xml
new file mode 100644
index 000000000..3b8552f6d
--- /dev/null
+++ b/test/samples/invalid/invalidresponseidentifier.xml
@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<assessmentItem xmlns="http://www.imsglobal.org/xsd/imsqti_v2p1"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://www.imsglobal.org/xsd/imsqti_v2p1  http://www.imsglobal.org/xsd/qti/qtiv2p1/imsqti_v2p1.xsd"
+	identifier="choiceMultiple" title="Composition of Water" adaptive="false" timeDependent="false">
+    <!-- identifier of responseDeclaration is invalid for QTI-SDK because it has a leading "space" char. -->
+	<responseDeclaration identifier=" RESPONSE" cardinality="multiple" baseType="identifier">
+		<correctResponse>
+			<value>H</value>
+			<value>O</value>
+		</correctResponse>
+		<mapping lowerBound="0" upperBound="2" defaultValue="-2">
+			<mapEntry mapKey="H" mappedValue="1"/>
+			<mapEntry mapKey="O" mappedValue="1"/>
+			<mapEntry mapKey="Cl" mappedValue="-1"/>
+		</mapping>
+	</responseDeclaration>
+	<outcomeDeclaration identifier="SCORE" cardinality="single" baseType="float"/>
+	<itemBody>
+		<choiceInteraction responseIdentifier="RESPONSE" shuffle="true" maxChoices="0">
+			<prompt>Which of the following elements are used to form water?</prompt>
+			<simpleChoice identifier="H" fixed="false">Hydrogen</simpleChoice>
+			<simpleChoice identifier="He" fixed="false">Helium</simpleChoice>
+			<simpleChoice identifier="C" fixed="false">Carbon</simpleChoice>
+			<simpleChoice identifier="O" fixed="false">Oxygen</simpleChoice>
+			<simpleChoice identifier="N" fixed="false">Nitrogen</simpleChoice>
+			<simpleChoice identifier="Cl" fixed="false">Chlorine</simpleChoice>
+		</choiceInteraction>
+	</itemBody>
+	<responseProcessing
+		template="http://www.imsglobal.org/question/qti_v2p1/rptemplates/map_response"/>
+</assessmentItem>