Cubase elements strange recording problem

I’m using cubase elements 6 on iMac with The last version of Mavericks with 2.7 i5 processor with 8 gb RAM. it was working fine. I have just uploaded all the wav files from a recent recording session at a different studio into a new project on my elements 6. I then did a basic mix. I then recorded some over dubs in the usual way. The recording was fine but then when I played back the track the following happened.

  1. The new track had digital distortion in it and when panned to the original position on the left lost all volume.
  2. The reverb send effect had changed and the delay time had increased to its maximum.
  3. Other guitar overdubs had also changed in the exactly the same way
  4. And really strangely, an early exported mix out of the same project had the same problems, ie the guitar track exhibited the same problems as the effected tracks in cubase.

I’ve looked in all the manuals and various forums and can’t find an example of this before. I’ve been recording for 10 years and never seen anything like this before. I’ve only been using the Firestudio for about a month and never had this problem before getting it. if anybody has any ideas, I would much appreciate the feedback.