fornatdate problems

Hi!

My question is wheather Xalan supports the method formatDate in ExsltDatetime packge of Xalan, according to its API-docs it should, but I cant get it to work for me.

I get following message whenever I try to execute that method:
javax.xml.transform.TransformerException: java.lang.NoSuchMethodException: For extension function, could not find method org.apache.xalan.lib.ExsltDatetime.formatDate([ExpressionContext,] #NODESET, #STRING).


I call it like this:
<xsl:value-of select="datetime:formatDate(./transmissionparts/TRANSMISSIONPART/period/PERIOD/start/TIMEINSTANT/@full, 'HH:mm')"/>

the first part being a string of a datetime. I'm able to other methods of this package, why cant I call this one?

best regards 

/Tomas