Automation Object Error Message

THE CONTEXT
I am building a personnel database to store various types of information on
staff. I have one table [tblStaff] at the centre of the database, describing
the member of staff (e.g. name, address, date of birth etc.). Another table
[tblPost] holds information on the posts/jobs the members of staff have. The
primary key in [tblStaff] is [StaffID]; [StaffID] is the foreign key in
[tblPost], linking the two tables together in a one-to-many relationship. I
have created seven other tables using the same principle, each describing a
separate aspect relating to a member of staff (e.g. training, expenses
claims, etc.). The only relationship each table has is to the [tblStaff]
table.

I want to collate the records from the various tables together into one
form. Ideally the user would be able both to add new records and edit
existing information through this one form.

To achieve this, I have created one lookup query for each table to lookup
the relevant information on the member of staff. I have created a form based
on each query, which I have then combined into a ‘master’ form using the
subform tool. Unfortunately, the ‘master’ form is not working.

THE PROBLEM
When I attempt to enter a value into the [tblPost] subform on ‘master’ form,
I am prompted with:

“The object doesn’t contain the automation object ‘tblStaff’. You tried to
run a visual basic procedure to set a property or method for an object.
However, the component doesn’t make the property or method available for
Automation operations. Check the component’s documentation for information
on the properties and methods it makes available for automation operations.�

The same error occurs irrespective of which field or subform I am trying to
fill on the 'master' form. Can anyone suggest why this might be?