xslt tokenize() and "Not a node item" error

I use tokenize() function to iterate through set of values, but then I try to use this values in template calls - "Not a node item" error occurs.

        <xsl:for-each select="tokenize($edge_pairs,';')">
                <xsl:if test="number(string-length(.)) &gt; 0">
                    <xsl:variable name="c_row" select="." as="xs:string"/>
                    <xsl:variable name="src" select="substring-before($c_row,':')" as="xs:string"/>
                    <xsl:variable name="dst" select="substring-after($c_row,':')" as="xs:string"/>
                        <xsl:call-template name="links">
                            <xsl:with-param name="src1" select="$src"/>
                            <xsl:with-param name="dst1" select="$dst"/>
                        </xsl:call-template>        
                </xsl:if>
            </xsl:for-each>

this is raw that triggers error:

<xsl:for-each select="root()//gml:edge[@source = $src1 and @target = $dst1 or  @source = $dst1 and @target = $src1]">