Referring to fields in tab controls

Hi all,

I am designing an Access form and want to change properties of one button when another button is clicked.

The button to be changed lives in an embedded tab control.

The button to be clicked is in a subform on the same tab control.

I have tried these:
[Forms]![ParentFormName].[tabName]![buttonName].Enabled = True
[Forms]![ParentFormName].[pageName]![buttonName].Enabled = True
[Forms]![ParentFormName]![tabName]![buttonName].Enabled = True
[Forms]![ParentFormName]![pageName]![buttonName].Enabled = True

None of which are recognised when I run the code.

Any ideas?

Thank you.