unable to set var using document function

I am trying to set a variable using the document function. 
 
<xsl:variable name="teamStandings"
select="document('MLB_TEAM_STANDINGS.XML')"/>
 
and then I try to retrieve something out of the xml
 
<xsl:value-of select="$teamStandings/sports-statistics/date/@year"/>
 
and it returns nothing.  If I do this, 
 
<xsl:value-of
select="document('MLB_TEAM_STANDINGS.XML')/sports-statistics/date/@year"/>
 
it returns 2002.  Is there something wrong with my syntax, or could it be in
the libxslt?  I didn't see anything specifically in the bug fix list that
seemed to address this, but I could be wrong.  Any suggestions would be
appreciated.
 
Gina

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