You can't have a multi-column text frame with variable width columns. Unchecking "Lock Column Guides" will allow you to reposition the COLUMN GUIDES not the text frame itself. Right now your text frame might be getting in your way, but if you move the text frame, you should be able to click on the COLUMN GUIDES and reposition them. I'd recommend moving these column guides on the Master Page so that the new guide setup will appear on all pages that are based on that Master Page. You can then create separate text frames linked together for each column on the Master Page. There are pros and cons to this. One con is that Span Columns can't be used with this method.
Ah, I see, so colums within a text frame all have to be the same width?
So the only way to acheive different column widths is to have a separate frame for each column?
(And then if I did want to span columns with a header I would need to put the head in its own frame)
Unfortunately yes. This is a downside to working with variable column widths.