[Asterisk-Users] Authentication Problem

[Neo]

Hello everbody,

I am having problems is Database version and Real time version of Asterisk.

Users are connecting with no problem,
they gets authenticate and its working fine,
but
after 2-3 minutes, registration with the same user comes and it gets 
failed to authenticate. dial tone gone, users unable to call,

but this behaviour not remains for the all users for all the time.

most of the time they are able to call,

its totally wiered to me.

any ideas ?

-Neo

p.s
i m using different kinds of clients
xlite
xpro
cisco ata
dta