The following XSLT macro saves without any errors, umbDebugShowTrace=true shows no errors, but the rich text editor renders an error.

It seems to error when attempting to GetMedia

<xsl:variable name="image" select="umbraco.library:GetMedia($thumbnail, 0)" />

Below is the full XSLT macro code

<?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" xmlns:ucomponents.cms="urn:ucomponents.cms" xmlns:ucomponents.dates="urn:ucomponents.dates" xmlns:ucomponents.io="urn:ucomponents.io" xmlns:ucomponents.media="urn:ucomponents.media" xmlns:ucomponents.members="urn:ucomponents.members" xmlns:ucomponents.nodes="urn:ucomponents.nodes" xmlns:ucomponents.search="urn:ucomponents.search" xmlns:ucomponents.strings="urn:ucomponents.strings" xmlns:ucomponents.urls="urn:ucomponents.urls" xmlns:ucomponents.xml="urn:ucomponents.xml"
  exclude-result-prefixes="msxml umbraco.library Exslt.ExsltCommon Exslt.ExsltDatesAndTimes Exslt.ExsltMath Exslt.ExsltRegularExpressions Exslt.ExsltStrings Exslt.ExsltSets ucomponents.cms ucomponents.dates ucomponents.io ucomponents.media ucomponents.members ucomponents.nodes ucomponents.search ucomponents.strings ucomponents.urls ucomponents.xml ">
  <xsl:output method="xml" omit-xml-declaration="yes"/>
  <xsl:param name="currentPage"/>
  <xsl:param name="thumbnail" select="/macro/thumbnail"/> <!--mediaCurrent-->
  <xsl:param name="video" select="/macro/video"/> <!--mediaCurrent-->
  <xsl:template match="/">
    <!-- start writing XSLT -->
    
    <xsl:if test="($thumbnail !='') and ($video !='')">
      <xsl:variable name="image" select="umbraco.library:GetMedia($thumbnail, 0)" />
      <xsl:variable name="vid" select="umbraco.library:GetMedia($video, 0)" />
      <a class="video-link" href="#player">
        <img alt="Play video" name="{$vid/umbracoFile}" src="{$image/umbracoFile}" />
      </a>
    </xsl:if>
  </xsl:template>
</xsl:stylesheet>

Any ideas?