I can't move my column guides (lock column guides in unchecked)

I can't move my column guides (lock column guides in unchecked)

I have created a text box with 4 columns, I want the first column to be wader than the other 3.

I have unchecked 'Lock Column Guides' (and double checked I have done this correctly!)

If I use either selection tool to try and drag the colun guides it just picks up and moves my entire text box.

What am I missing? Sorry if it's obvious, it's driving me mad!

Thanks