System.Xml.Xsl.XslTransformException: An error occurred during a call to extension function 'GetMediaUrl'. See InnerException for a complete description of the error. ---> System.FormatException: Unrecognized Guid format.
   at System.Guid.GuidResult.SetFailure(ParseFailureKind failure, String failureMessageID, Object failureMessageFormatArgument, String failureArgumentName, Exception innerException)
   at System.Guid.TryParseGuid(String g, GuidStyles flags, GuidResult& result)
   at System.Guid.Parse(String input)
   at Sitecore.Resources.Media.MediaProvider.GetMediaUrl(MediaItem item, MediaUrlOptions options)
   at Sitecore.Xml.Xsl.XslHelper.GetMediaUrl(XPathNodeIterator iterator, Boolean useItemPath, String parameters, Boolean xhtml)
   at Sitecore.Xml.Xsl.XslHelper.GetMediaUrl(XPathNodeIterator iterator)
   --- End of inner exception stack trace ---
   at System.Xml.Xsl.Runtime.XmlExtensionFunction.Invoke(Object extObj, Object[] args)
   at System.Xml.Xsl.Runtime.XmlQueryContext.InvokeXsltLateBoundFunction(String name, String namespaceUri, IList`1[] args)
   at <xsl:template name="PrintSocialGraph">(XmlQueryRuntime {urn:schemas-microsoft-com:xslt-debug}runtime, XPathNavigator {urn:schemas-microsoft-com:xslt-debug}current)
   at <xsl:template match="*">(XmlQueryRuntime {urn:schemas-microsoft-com:xslt-debug}runtime, XPathNavigator {urn:schemas-microsoft-com:xslt-debug}current)
   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 Mvp.Xml.Common.Xsl.MvpXslTransform.TransformToWriter(XmlInput defaultDocument, XsltArgumentList xsltArgs, XmlWriter xmlWriter)
   at Mvp.Xml.Common.Xsl.MvpXslTransform.Transform(XmlInput input, XsltArgumentList arguments, XmlOutput output)
   at Sitecore.Web.UI.WebControls.XslFile.DoRender(HtmlTextWriter output, Item item) Xsl file could not be processed: /ux15/xsl/head_tag.xslt