Welcome, and thanks for joining.
Something to check though, do you have the lens firmly clicked into place? I presume that you have detached the lens and re-attached? It sounds like you only have one lens but if you can borrow one and try that you will be able to determine if it is the lens or the camera...john
Just to add, if you can, go to a camera store, explain your situation, and ask if you can check with one of their lenses, if it works. If it says that there's an error, still, then the problem is with the camera. If there's no problem, then try the lens on other Konica Minolta / Sony cameras, if they say error, then there's a problem with the lens.
Usually, this error is associated with older Sigma lenses, not an 18-70mm lens. I assume it's a Sony 18-70mm lens.
Hope this helps. Let us know how you get on.