All backups to a CIFS share hosted on a ReadyNAS 2100 kick off and run as expected for a certain length of time before failing with the following error message: "Error Message: 2129 - can't write cifs:xxx;email@example.com/vRanger$/Production/asff1_421be088-4307-7ebe-fffd-51de456e5079/ksqlp1_20135422_230019_a835fdd6-81de-4beb-9725-763081af93f8/.a05fb76f-9743-45d7-85de-e228b7092fe1/.a05fb76f-9743-45d7-65de-e22ht7092fe1.var." This happens consistently after a certain period of time, 30 minutes for example.
In ReadyNAS firmware version 4.2.19 there is a section where user accounts are configured. There are a multitude of settings there, among them are Block Limits and Block Quotas for the accounts that are permitted access. If the account vRanger is using to access the device is configured with the default block quota (4GB) and vRanger writes enough data to the device to hit that quota the job will terminate with the above error message.
In this version of the ReadyNAS firmware there is an option to either configure a larger block quota or enter a zero in the box which will turn off the quota for the vRanger account. Either of these would be a valid workaround.