saxon error: using format-number

I am using format-number to display my prices with a comma and a dot,
like 21,200.35.

Here is a sample XML:

<xslnumbers>  
<numbers>10,000.66</numbers>  
<numbers>1,300.88</numbers>  
</xslnumbers>

The XSL is:

<P>  
<xsl:value-of select="//numbers[1]"/>  
<xsl:text> + </xsl:text>  
<xsl:value-of select="//numbers[2]"/>  
<xsl:text> = </xsl:text>  
<xsl:value-of select="format-number(translate(//numbers[1],',','') +
translate(//numbers[2],',',''),'###,##0.00')"/>
</P>  

Resultant HTML in Stylus:
10,000.66 + 1,300.88 = 11,301.54

Though I get the desired output in Stylus, Saxon gives me a
"number-format function: locale not registered" error.
I am using a older version of Saxon is that what is causing the problem?

TIA
Seema


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