>Any pointers ?

See my sig.

Or if you prefer, read the spec

http://www.w3.org/TR/xslt20/#format-date

You can convert anything to a string using the string() function. Specifying as="xs:string" doesn't convert it to a string, it asserts that it already is a string.

By the way, make sure you are using Altova 2008. The 2007 edition didn't support format-date() properly.

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference