[xsl] Error: sequence of more than one item not allowed

["Mark" <mark@xxxxxxxxxxxx>]

Of the two nearly parallel statements below, (2) raises the error: "Sequence 
of more than one item not allowed as the second operand of 'eq'."

(1) groups-by the attribute ($format) and (2) by all the not ($format) 
attributes found in <Formats>. My thinking was that in (2) the 'group-by' 
would return a current-group() resolved to a single attribute by the 
<xsl:for-each select"current()> statement, but if so, I am clearly 
addressing that single attribute incorrectly. On the other hand, no error is 
reported when in (2) the group-by="@*[not(name(.)=$format)] resolves to a 
single attribute. Can I specify the <xsl:if test="$item eq ???"/> to avoid 
this error in (2) and still test against all of the not($format) attributes?

Thanks,
Mark

(1)
<xsl:for-each-group select="../../Stamp/Formats" 
group-by="@*[name(.)=$format]">
           <xsl:for-each select="current-group()">
             <xsl:if test="$item eq @*[name(.)=$format]"> <!--No error -->

(2)
<xsl:for-each-group select="../../Stamp/Formats" 
group-by="@*[not(name(.)=$format)]">
           <xsl:for-each select="current-group()">
             <xsl:if test="$item eq @*[not(name(.)=$format)]"> <!--  
Error -->