Date problem: StringIndexOutOfBoundsException when parsing

Hi,

i have a problem with formatting date, my xml part where i got the
date looks like this:
 <dateCreated>2008-01-04T15:02:57.72Z</dateCreated>

if I use the code below, i get the following error message from xsl-fo
(Location of error unknown)java.lang.StringIndexOutOfBoundsException:
String index out of range: 0

if I however change the code so date it takes the variable $someData
instead of dateCreated[node()] as input, it all works fine
To me it shouldnt be any difference....i would appreciate any tips for
what might be wrong, or alternative solutions
what i want to do is take the date and format it into something nicer,
e.g. turn it into
"Thu, 04.01.2008, 15:02"

<xsl:variable name="someData"
as="xs:dateTime">2008-01-04T14:34:07.868Z</xsl:variable>

<xsl:call-template name="format-date">
     <xsl:with-param name="dateString" select="dateCreated[node()]"/>
</xsl:call-template>	


	<xsl:template name="format-date">
	    <xsl:param name="dateString"/>
		<xsl:value-of select="date:day-in-month($dateString)"/>
	</xsl:template>