Error while concatenating a string to variable in xslt

Please Help me with this code, It gives an error of "too many items" in line 3:

<xsl:when test=".[@name='Measurement Pallete']">
    <xsl:variable name="controlID" select=".[@name='Measurement Pallete']/Control/@id"/>
    <xsl:variable name="control_ID" select="translate($controlID, ' ', '')"/>
    <xsl:variable name="funcName" select="concat('ClassicTab', $control_ID)"/>              
</xsl:when>