Error getting index: Previous backup index is offline

As we see from the backup selection is looking for a previous index, my guess is it could be Dump1, etc ( incremental ) these are the jobs which needs previous Full backup indexes to be online

My followup question would be whether the indexes of the Full backup or DUMP0 is it still online and not expired, if not expired you can 

To load offline indexes:
1 In the Navigation pane, click Create Restore Job, and then on the Choose Saveset page, click Manage
Indexes.
2 Click Choose Client, and select the client for which the backup was created.
-or
quickly locate the client (s), you can use the Search box at the upper right corner of the table. The data
in the table is filtered as you type the search text into the box.
3 Click OK to close the dialog box.
4 Optionally, click Choose Plugin, and select the plug-in that was used to create the backup. Click OK to
close the dialog box.
5 Click the View icon to list the savesets for the selected client and plug-in.
6 In the savesets list, all items are selected by default.
To load indexes for specific savesets, clear the checkmarks for the savesets that you want to exclude.
Alternatively, click the checkbox in the header row to remove all checkmarks, and select the individual
savesets.
7 Click Load, and in the Load Index dialog box, configure the following option:
 Days to Keep Index: Type or select the number of days you want to store the index in the NetVault
Database. By default, the index is retained for one day.
8 Click OK to close the dialog box

Refer https://support.quest.com/technical-documents/netvault/13.0/administration-guide/45#TOPIC-1432700

As we see from the backup selection is looking for a previous index, my guess is it could be Dump1, etc ( incremental ) these are the jobs which needs previous Full backup indexes to be online

My followup question would be whether the indexes of the Full backup or DUMP0 is it still online and not expired, if not expired you can 

To load offline indexes:
1 In the Navigation pane, click Create Restore Job, and then on the Choose Saveset page, click Manage
Indexes.
2 Click Choose Client, and select the client for which the backup was created.
-or
quickly locate the client (s), you can use the Search box at the upper right corner of the table. The data
in the table is filtered as you type the search text into the box.
3 Click OK to close the dialog box.
4 Optionally, click Choose Plugin, and select the plug-in that was used to create the backup. Click OK to
close the dialog box.
5 Click the View icon to list the savesets for the selected client and plug-in.
6 In the savesets list, all items are selected by default.
To load indexes for specific savesets, clear the checkmarks for the savesets that you want to exclude.
Alternatively, click the checkbox in the header row to remove all checkmarks, and select the individual
savesets.
7 Click Load, and in the Load Index dialog box, configure the following option:
 Days to Keep Index: Type or select the number of days you want to store the index in the NetVault
Database. By default, the index is retained for one day.
8 Click OK to close the dialog box

Refer https://support.quest.com/technical-documents/netvault/13.0/administration-guide/45#TOPIC-1432700