why samba share files are not able to access by some user for some time?

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http://askubuntu.com – I'm running samba on Ubuntu Server 10.04 LTS, I've some folders on samba share and created some user to access it, but suddenly some of the user are not able to access it for a certain time only. For i.e: There are 5 users as A,B,C,D,E and there are two folders in samba share name as "test" and "develop" "test" doesn't have any user access password but "develop" has user access with password. Now A,C,E are able to access folder "develop" with their samba password but B,D are not able to access with their samba password for some time only or if I use B-username & password in A or C la (HowTos)