Error parsing the XSLT:

System.Xml.Xsl.XslTransformException: Cannot find a script or an extension object associated with namespace 'urn:Exslt.ExsltStrings'. at System.Xml.Xsl.Runtime.XmlQueryContext.InvokeXsltLateBoundFunction(String name, String namespaceUri, IList`1[] args) at (XmlQueryRuntime {urn:schemas-microsoft-com:xslt-debug}runtime) at Root(XmlQueryRuntime {urn:schemas-microsoft-com:xslt-debug}runtime) at System.Xml.Xsl.XmlILCommand.Execute(Object defaultDocument, XmlResolver dataSources, XsltArgumentList argumentList, XmlWriter writer) at System.Xml.Xsl.XslCompiledTransform.Transform(IXPathNavigable input, XsltArgumentList arguments, TextWriter results) at umbraco.macro.GetXsltTransformResult(XmlDocument macroXML, XslCompiledTransform xslt, Dictionary`2 parameters) at umbraco.presentation.umbraco.developer.Xslt.xsltVisualize.visualizeDo_Click(Object sender, EventArgs e)

I have not made any changes to the XSLT file and it was was working fine. 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE xsl:stylesheet [ <!ENTITY nbsp "&#x00A0;"> ]>
<xsl:stylesheet
  version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:msxml="urn:schemas-microsoft-com:xslt"
  xmlns:umbraco.library="urn:umbraco.library" xmlns:Exslt.ExsltCommon="urn:Exslt.ExsltCommon" xmlns:Exslt.ExsltDatesAndTimes="urn:Exslt.ExsltDatesAndTimes" xmlns:Exslt.ExsltMath="urn:Exslt.ExsltMath" xmlns:Exslt.ExsltRegularExpressions="urn:Exslt.ExsltRegularExpressions" xmlns:Exslt.ExsltStrings="urn:Exslt.ExsltStrings" xmlns:Exslt.ExsltSets="urn:Exslt.ExsltSets"
  exclude-result-prefixes="msxml umbraco.library Exslt.ExsltCommon Exslt.ExsltDatesAndTimes Exslt.ExsltMath Exslt.ExsltRegularExpressions Exslt.ExsltStrings ">

<xsl:output method="xml" omit-xml-declaration="yes"/>

<xsl:param name="currentPage"/>

<xsl:template match="/">
  <xsl:variable name="sidebarNode" select="$currentPage/ancestor-or-self::* [@isDoc][string(sidebarFeatures)!=''] [position()=1] " />
  <xsl:for-each select="Exslt.ExsltStrings:split($sidebarNode/sidebarFeatures, ',')">
    <xsl:variable name="node" select="umbraco.library:GetXmlNodeById(.)"/>
    <xsl:value-of select="umbraco.library:RenderTemplate($node/@id, $node/@template)" disable-output-escaping="yes"/>
  </xsl:for-each>
</xsl:template>

</xsl:stylesheet>