setting parameters on XSLT Prozessor

Hi, 

in my JavaScript I set 2 parameters in the XSLT that I declared with 

<xsl:param name="gSelectedNode">/root</xsl:param>
<xsl:param name="sChannel"></xsl:param>

var objXSLTProc = new XSLTProcessor();
objXSLTProc.setParameter("",varName, value)

function. varName holds the Name of the parameter. Now on testing the
parameters in XSLT one works and one not. The first one ist tested with

<xsl:choose>
	<xsl:when test="$gSelectedNode = '/root'> .....</xsl:when>
	<xsl:when test="$gSelectedNode = '/root/channel'> .....</xsl:when>
</xsl:choose>

the other one in a for-each statement
<xsl:for-each select="//root/channel">
	<xsl:if test="$sChannel=@address">...</xsl:if>
</xsl:for-each>

the .xml looks like this

<root>
  <channel address="0">
    <signal address="0">
      <filttype>0</filttype>
      <filtfreq>10000</filtfreq>
      <outputrate>9600</outputrate>
    </signal>
</root>

If I exclude the <xsl:if> with the second parameter test, it all works
fine. Else the transformation is empty.

Where do I get Error Messages from the Prozessor? There not in the returned
empty documentFragment and not in the JavaScript Error Console.....

thx in advance
Sebastian