File:New generates error

Hi,
We have strange error started coming recently for using java A=
PI to check file existence. Recently we moved to saxon and earlier we were 
using Xalan but I dont think this caused the error. We were using this code
since years or so without any problem and this error =A0comes randomly. I 
am not able to replicate this in dev environment. I would appreciate your 
help on finding root cause of this problem.

XSL Code:

<xsl:template name="file-exists" xmlns:file="java.io.File">

		<xsl:param name="filename"/>
		<xsl:choose>
			<xsl:when test="file:exists(file:new($filename)) = 'true'">true</xsl:when>
			<xsl:otherwise>false</xsl:otherwise>
		</xsl:choose>
	</xsl:template>

Error:
ERROR:  'Cannot convert argument/return type in call to method 'java.io.File.new(reference)''

FATAL ERROR:  'Could not compile stylesheet'

 

java.lang.ClassCastException: com.sun.org.apache.xalan.internal.xsltc.compiler.Variable cannot be cast to com.sun.org.apache.xalan.internal.xsltc.compiler.Param

      at com.sun.org.apache.xalan.internal.xsltc.compiler.SymbolTable.addParam(Unknown Source)