'play' is not a valid instance name

Have just made the move from Flash CS3 to CS5
When I open one of my cs3.fla’s and save it as a cs5.fla and then export I’m getting the following output message.

‘play’ is not a valid instance name. Please enter an identifier that is not a reserved keyword or function.

This only happens when I export it for the first time after opening it (if I close that file down and open it again I get the same message)

I dont have any clips with the instance name ‘play’ or anything like that

does anyone know why I’m getting this message??

I’m currently using AS2