Some VMware Data Recovery backup jobs are not completing. What could cause this?

A.
4 GB of free space on the DR datastore

B.
Four backup jobs are running

C.
Four restore jobs are running

D.
ESXi host processor utilization above 90%

Explanation:
http://pubs.vmware.com/vsphere-50/index.jsp?topic=/com.vmware.datarecovery.admin.doc_20/GUID-A1A9D274-44EA-4237-A8DE-46D01CCE673E.html

Backup and restore operations are not completing as expected.
An integrity check may have discovered a problem with the integrity of the deduplication store.
The integrity of new backups is checked each day, and the entire deduplication store is checked once a week. If problems are found during the integrity check, the deduplication store is locked. As a result, no backups or restores can be performed until the issues reported by the integrity check are fixed. To resolve this issue, select the problematic restore points on the restore tab, and click Mark for Delete. These restore points are deleted during the next integrity check, after which the deduplication store is unlocked.
If no integrity check problem has been identified, the issue may be due to an excess of jobs. Data Recovery limits the number of jobs that can run to help prevent systems from becoming overloaded and failing to make progress. Some of the limits include:
Maximum of eight backup jobs can run at the same time.
Maximum of eight restore jobs can run at the same time.

Processor utilization must not exceed 90% to start single backups or 80% to start multiple backups.
The datastore where virtual machines are located must have at least 10 GB of space for indexing and processing restore points and 5 GB of storage space available for each virtual machine to be backed up. For example, to simultaneously back up eight virtual machines that reside on one datastore, 50 GB of storage space should be available with 10 GB for indexing and processing and 40 GB for the virtual machines.
If any of these limits are exceeded, new jobs do not start.