File Share access by MAC on Windows server 2003

Hi everyone,
i have windows 2003 server installed, and for some reason my Mac can't
access the share folders, so i search in google and i found than i need to
modify the registry.
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\LanManServer\Parameters
The value of RequireSecuritySignature needs to be changed from '1' to '0'.

It works but the problem is that it keeps changing back during the day to
the default value.
how can i fix this problem?

Thanks