MS Access gives right truncated (null) message


I'm getting the following message when I try to add multiple records to my
MS Access table:-

'String data, right truncated (null)'

The message appears even when I try to add a record with exactly the same
data as the first.
Three of the fields are Access memo fields, If I don't populate these
fields, then the insertion works ok.

I'm populating my table from an (AS/400) dataset, so i'm making repeated
calls to TQuery.ExecSql. the TQuery component has an SQL property of 'Insert
into etc...'. The first call works, all subsequent calls fail - even using
the same data.

The query is a parameterised query and i'm using Param[i].AsMemo to bind the
I've tried clearing out the parameters after the first ExecSQL but this
makes no difference.

Using Delphi 5 with patch, and going to Access database via ODBC driver.

The data inside the memo fields is not that large, maybe a few hundred
characters erach field.

Any ideas anybody please? - i'm stumped!