I think you must have had quotes around the path as in
Code:
<xsl:variable name="SZ" select="'//n:Envelope/x:body/x:RE/x:RE_1d/x:Ive'" />
or possibly you're passing a string as an input parameter otherwise it would work.
In general what you want though is not possible under standard XSLT.
Some processors, Saxon for example, provide an evaluate extaension to cope with this otherwise you can write an extension using script if you're using MSXML, .NET if using .NET XSL or Java for other Java based processors.
--
Joe (
Microsoft MVP - XML)