update taxonomy field by webservice

Hi All,

i have a list which one of the field is a Taxonomy field. while updating this fields by Webservice List.asmx i faced two things

1. when i have WSSID (i.e. taxonomy exists in TaxonomyHiddenlist) it is working fine by putting the input field as 

2. when the Taxonomy item not exists in TaxonomyHidden list. whileupdating nothing happening.

<Field Name="Tax_x0020_File_x0020_Type">-1#Fees|407c0653-42cd-48bb-beed-2cb0079dbccf</Field>

Note

i put -1 instead off the WSSID as it is not exists in TaxonomyHiddenlist