2.6.8 won't run on my Macbook air

[Timoshev]

Any suggestions why 2.6.8 won't run on Mac?  I previously used 2.6.4 OK on same machine.

It's possible the work IT bods have changed something but don't think so.  I did see reference to deleting files 
...   http://www.videohelp.com/tools/AviDemux  .... but my system won't allow me to move rename or delete them.

Regards
Tim