Hello Bonnie,
Thanks for your reply,
This issue occurred in all transaction and all users are affected. It was happened only for several hours. I've checked the system log, there's nothing abnormal. I've try to login again on the next day, everything was back to normal. any idea? If this is a sapgui issue, i think only the particular user with problematic sapgui encountered it, but for this issue, all user were affected.
Regards,
Z