what does the error 1015 mean?

the error code 1015 appeared when i tried to restore original setting of my 3g i phone. i tune recommended to update software version. when it did so, a message showed that system had to be restored. while restoring, the error appeared on i tune. now, i can't use my phone. i tune was updated as recommended by the site to eleminate one of the factor that might be the cause of the error.

for those who encountered the same problem, would u plz HELP. thanks in advance.