Could this be a hack attempt?

[phpknight]

Hi,

 

I've had this code that has been working for about five years.  Then, out of the blue today, I get this error a few times:

 

Warning: session_start() [function.session-start]: The session id contains illegal characters, valid characters are a-z, A-Z, 0-9 and '-,'

 

The weird thing is I am not supplying a name, and I haven't upgraded PHP lately or anything that might cause this.  So, the question is: could this be a hack attempt by somebody trying to supply a bad session id from the client side?

 

And, would there be any way to test if the warning was triggered and see what ID is actually causing this?  I'm familiar with catching errors but not warnings.

 

Thanks!