Cubase LE5 Audio Activity Bar at Full when input bus added


Using Cubase LE5 on a Mac, have a problem when connecting up my audio interface was wondering if anyone might be able to help?

As usual I connect my interface and select it in device setup. The problem occurs when I go to VST Connections and add an input bus. At this point the input audio activity bar on the transport panel goes to full and clips, it then freezes in this position. I can add tracks and track but nothing is recorded.

I’ve been using the same interface for a year or so and have not had this problem before. The interface functions fine with another DAW.

Can anyone help?
Thanks in advance