I have a Samba (Version 4.1.6-Ubuntu) DLC (Server role: ROLE_ACTIVE_DIRECTORY_DC) on an Ubuntu Server (Ubuntu 14.04.1 LTS)
Several Windows 7 Professional Clients are connected every day and usually everything works fine. To keep the roaming profiles as small as possible, folders like the Desktop, Documents etc. are redirected to network shares. At random points (it can happen once a day, or more often, sometimes it even works well for a couple of days) the Windows Client (different ones and at different times) seem to loose connection, the whole system freezes since it's trying to access the server but somehow not able to. Nevertheless, the server is available and pingable, even accessing via putty is possible. Seamlessly, the network share seems to be not accessible. By investigating the logs I found a warning 'Security-Kerberos' (EventID: 14) where it is saying that the stored credentials are not valid anymore.
On the server side I can find a lot of entries like this:
Feb 9 10:07:42 FHS smbd[15130]: [2015/02/09 10:07:42.350858, 0] ../source3/smbd/uid.c:153(check_user_share_access)
Feb 9 10:07:42 FHS smbd[15130]: user XXX\XXX$ connection to folder denied due to share security descriptor.
Feb 9 10:07:42 FHS smbd[15130]: [2015/02/09 10:07:42.352567, 0] ../source3/smbd/uid.c:153(check_user_share_access)
Feb 9 10:07:42 FHS smbd[15130]: user XXX\XXX$ connection to folder denied due to share security descriptor.
Feb 9 10:07:42 FHS smbd[15130]: [2015/02/09 10:07:42.353559, 0] ../source3/smbd/uid.c:153(check_user_share_access)
Feb 9 10:07:42 FHS smbd[15130]: user XXX\XXX$ connection to folder denied due to share security descriptor.
Feb 9 11:16:39 FHS smbd[15527]: [2015/02/09 11:16:39.990222, 0] ../source3/param/loadparm.c:4365(process_usershare_file)
Feb 9 11:16:39 FHS smbd[15527]: process_usershare_file: stat of /var/lib/samba/usershares/hom failed. Permission denied
Feb 9 11:16:39 FHS smbd[15527]: [2015/02/09 11:16:39.994208, 0] ../source3/param/loadparm.c:4365(process_usershare_file)
Feb 9 11:16:39 FHS smbd[15527]: process_usershare_file: stat of /var/lib/samba/usershares/hom failed. No such file or directory
I don't know if this is related but I assume so. Is it possible that after some time the windows client 'forgets' the credentials? Because the server certainly does not change them. After a restart of the client everything usually works fine again.
There was another question asked which might be related to this.