Recently out of the blue (I didn't make any changes) my customers have been getting this error message when submitting their info:

(97) This transaction cannot be accepted.

So I went on the chat ant they told me to enter my x_fp_timestamp on this website: http://developer.authorize.net/tools/responsecode97/

Anyway I went into my php (SIM) code and this is all I have for the variable:  

$sequence=time();
$tstamp=time();

There's no numbers to put in or anything. I guess I'm really confused as to what to put into the request form and in general why I would just get this error out of the blue?

Any feedback/help/assistance would be greatly appreciated.

Thanks