[xsl] Strange error: Unknown collation

["peter verhaar" <peter.verhaar1@xxxxxxxxx>]

Hello,

The following 2 lines:

                <xsl:variable name="notImportant" select="(1,2)"/>
                <xsl:variable name="errorProducingLine"
select="sum(for $a in $notImportant return number(max(1,2)))"/>

Are producing an error/warning on the closing bracket of the second line:

Error: FOCH0002: Unknown collation
Warning: SXWN9001: A variable with no following sibling instructions
has no effect

But if I remove the Max and change this to something else, it works fine!

                <xsl:variable name="errorProducingLine"
select="sum(for $a in $notImportant return number(1+1))"/>

What's wrong with that first second line?

Thanks! Peter