I am having problems converting an xml file containing MathML entities to html - the following is a segment of the input.....

 <!ENTITY Fopf  "&#x1D53D;" ><!--/Bbb F, open face F -->

 <sect2 id="eap017-sec2-0001">
 <title>The Characteristic of &Fopf;</title>
 <p>Since a field is closed under addition, &Fopf; contains

The is no problem when I render the title directly - the entity is output in the html as &#120125 (there is a post-processing stage that replaces these wth images)
However, later in the process, I need to create a href to this title - the following is a summary of the xsl code (not an exact replica, for the sake of clarity) 
    <xsl:variable name="title">
      <xsl:apply-templates select="."/>
    <xsl:variable name="link-title" select="string($title)"/>
    <a href="{$href}">
       <xsl:value-of select="$link-title"/>

The following is the run-time error I get:
Output character not available in this encoding (decimal 55349)
However, if I do <xsl:message><xsl:value-of select="$link-title"/></xsl:message> I see the title output correctly:
The Characteristic of &#120125;
I have to admit I know very little about character sets, Unicode, etc - any ideas what the problem is?