Weird issue with ASIO in Cubase 4

I’ve been using Cubase 4 on my Mac Pro for ages with relatively few problems. However, this afternoon i went to import an audio file and auto-play failed to start. As most of you know, selecting an audio file with auto-play engaged normally means the audio starts playing and the playhead in the little import box starts running from left to right. This didn’t happen, nor did the audio play.

This has happened very occasionally in the past. When it happens all i do to get it running again is switch the sample rate of my audio interface from 48 to 44 then back again. For whatever reason that always seems to sort it out. Today though, doing this would only allow me to click on one file to import (it would auto-play and be heard) before going silent again.

After a lot of quitting/restarting and generally wasting stupid amounts of time i finally noticed that the minute this happened i was also getting constant ASIO overload. In other words the ASIO meter would sitting right down at the bottom until i went to import for a second time, where it would then trigger the overload light (even though the ASIO level barely moved).

I can’t for the life of me work out what is wrong. I’m running a pair of Prism Orpheus convertors - everything normally runs absolutely fine but for some reason today this has started happening. I’ve spent hours trying to sort it.

Can anyone offer any help on this ?