[Zope] Update a database from a FORM gives missing input variable

[neil_b@yahoo.co.uk]

I am close to getting a form to update a database, but I seem to have 
misunderstood how ZSQLMethod gets variables:

The Form:

<form action="update_table">
<input type="hidden" name="PeopleID" value="9999">
<input type="text" name="Surname" value="">
<INPUT type="submit" value="save" name="submit">
</form>

The action method:

<dtml-call sql_update_tblPeople>

Finally the ZSQLMethod (no arguments set):

UPDATE tblPeople SET tblPeople.Surname = <dtml-sqlvar Surname 
type="string">
WHERE tblPeople.PeopleID = <dtml-sqlvar PeopleID type="int">

>From all the documentation and How-tos I have read so far, this 
should work, but I get:

missing input variable Surname

Changing the update_table method to:

<dtml-var Surname>

shows that the form delivers the right value.

Can anyone help me to spot my silly error?

TIA

Neil