UserInterfaceOnly Issues....new issue (I think)

I have a sheet which has protection on the workbook and on the sheets. It uses autofilter and also outlining, and the vba needs to read and write some cells.
Currently I have "nested" protect/unprotect routines. I was trying to utilise UserInterfaceOnly in order to economise the code, but it is not working.
In fact, when I input the code, the keyword is not even being capitalised!!
The boolean parameter is being capitalised and the text colour changed to blue, as per normal, but there is no capitalisation on the UserInterfaceOnly statement, and the statement appears to have no effect in the code. Here is the relevant line of code.....

For Each ws In ThisWorkbook.Worksheets
    With ws
    .Protect Password:="*****", AllowFiltering:=True, userinterfaceonly:=True
    .EnableOutlining = True
    End With
Next ws

This is in the Workbook_open() module. What am I doing wrong? Why is the parameter not capitalising as it should and why is it not effective?
I have searched everywhere to see if his problem is common or if I am using the wrong syntax and can't seem to find anything.

Greatly appreciate any assistance.
Thanks.
Littlenuts......