Subform won't create new record (Access 2007)

If you open your subform directly, can you then add new records?

In most cases, this behavior is due to (a) invalid, non-updateable query on the subform or (b) invalid Master/Child links between the Main and Subform. This can also be the result of improper table structures (i.e. if you haven't correctly structured the Parent/Child relationship between the tables driving the Main/Child form).

The query that you have for your main is far too complex for the job and as a result will not allow addition of records. You have a relationship between tbl_treatment and tbl_subformtreatment that just shouldn't be there (it can't add a treatment until there's a matching entry in the subformtreatment table, which can't be entered until the treatment is added ...)
Just drop tbl_Subformtreatment from your form's query and you'll be able to add records. To get data from tbl_Subformtreatment to use in calculations on the main form use DLookUp()
You also don't need tbl_Patients in your form's query:
- make the source of your patient selection combo:
SELECT ([tpfirstname]) & " " & ([tpsurname]) as Patient, tbl_Patients.tpPatient FROM tbl_Patients ORDER BY tbl_Patients.tpFirstname;
- Set the Bound column = 2
- Set the column count to one
- make the combo big enough to display the name
- delete the text box Text45

Thanks MikeToole,

I tried the following:

>Just drop tbl_Subformtreatment from your form's query and you'll be able to add records.

I removed tbl_subformtreatment from qry_treatments (the main form's query), however I'm still not able to add records to the subform. The error message I'm getting is:

"You can't assign a value to this object
*The object may be a control on a read only form
*The object may be on a form that is open in design view
*The value may be too large for this field"

(You should be able to see this message yourself when you view my sample database).

Am I missing something?

Thanks for taking the time to go into so much detail it was a great help. You're a legend.

We were facing a similar issue when a client approached us with the problem that they could not create new child record in a subform in a situation where there were not **already any exsiting child records** for the master record.  The solution was to set the correct "Trust Centre Settings" in Access 2007 - this may also be worth checking in addition to the points above.