user manager error

dear all,

i have a little difficulty with user manager, i can not go to maintenance menu.
everytime i click maintenance, the errors are :

Invalid/unknown response from server:

Network Error
Network Error (tcp_error)

A communication error occurred: "Connection aborted"
The Web Server may be down, too busy, or experiencing other problems preventing it from responding to requests. You may wish to try again at a later time.

For assistance, contact your network support team.

after the OK clicked, and than click Maintenance one more time, the next message is

Your session has been reset due to inactivity.

i try to remove user-manager package and reinstall it, but the same problem still persist.

can anyone let me know what to do ?
i can not do database backup

TIA

Paul

problem solved !!
but i still does not know the correspondence between an error and the problem source.

it caused by inserted micro-sd error.
once the micro-sd un-plug, the error disappear

can anyone see the correspondence of this problem ?

Paul