Queries :: Sub-queries With Text Box Based Parameter

I'm trying to perform a DELETE query at run-time. The criteria for deleting records is somewhat complex due to various one-to-many dependancies between the tables, overlapping of date fields etc., so in order to restrict the DELETE to only those records which qualify, I've set up a load of smaller queries to produce the list of eligible records.There is only one parameter required - a 'CutOff' date which is arbitrarily chosen by the user and is available in a textbox control on an open form when the code is triggered.

Here is the main DELETE query :

Code:
DELETE DISTINCTROW [tblComments].*
FROM [tblComments]
INNER JOIN [qryCommentsToPurge]
ON [tblComments].[CommentID] = [qryCommentsToPurge].[CommentID]
WHERE [tblComments].[CommentID] = [qryCommentsToPurge].[CommentID]

I've put qryCommentsToPurge and all the cascading sub-queries below - have highlighted in red where the parameter value is required (it is used in the queries to identify the records which must be retained, i.e. not deleted)Each of the individual sub-queries works fine and correctly (they return the correct population of records that they were designed to)If I run the sub-queries manually, I am prompted to provide the CutOff date, as you would expect - and the recordset returned in each case is correct for that date.

If, however, I run the DELETE at run-time (with the form containing that textbox open and containing a valid date value) I get a 3061 error :Suggesting that the queries can't pull the parameter value from the textbox on the form. But I've stuck a watch in the debugger on [Forms]![frmArchive]![txtCutOffDate] and I'm getting the correct date value? The form is open and available at the time.So why can't the query see it? I use these kinds of control references elsewhere in other queries and they work fine. I don't understand why it's a problem here?

Code:
SELECT [tblComments].*
FROM [tblComments]
INNER JOIN [qryIssuesToPurge]
ON [tblComments].[IssueID] = [qryIssuesToPurge].[IssueID]
ORDER BY [tblComments].[CommentID];

[code]...