When you first install MSCS, the Cluster Service is granted all the rights necessary to function. If you every have to re-create the Cluster Service account, you must manually grant these rights.
You must use a domain account that is a member of the local Administrators group on each node in the cluster. You can use
User Manager for Windows NT 4.0, or Computer Management for Windows 2000, or
NET Localgroup Administrators
The following rights are required on all nodes in the cluster:
Act as part of the operating system (only required with Windows 2000). Back up files and directories. Increase quotas. Increase scheduling priority. Load and unload device drivers. Lock pages in memory. Log on as a service. Restore files and directories.To grant these rights for Windows NT 4.0, use User Manager / Policies / User Rights, making sure you select Show Advanced User Rights.
For Windows 2000, use Local Security Policy / Security Settings / Local Policies / User Rights Assignment.
See Knowledge Base article Q254219 - Security Considerations When Implementing Clustered File Shares.