I've found a topic but...not in english...and I've understand that is may be a problem due a recent release of Jpgraph.
I've found these correction :
sscanf($list[8],"%4d%1s%2d%1s%2d%2d%1s%2d%1s%2d",$a_year,$nul,
$a_month,$nul,$a_day,$a_hours,$nul,$a_minutes,$nul,$a_seconds);
to apply to grph ...