never include query tag in syntax
try this
string camlquery = @"<Where><Eq><FieldRef Name="Vendor_x0020_Product_x0020_Name"/>
<Value Type="Text">" + xpathresultBTADSLMAX + @"</Value>
</Eq>
</Where>";
further details you can see this artical http://rmanimaran.wordpress.com/2011/03/11/new-in-sharepoint-2010-caml-query/
hops its helps..