Hi Carlo, 

It seems one or some of the search domains are corrupted. Could you please check which search domains you are searching against first and then from Search Domains window, see if those domains are all active and have any un-synchronized documents. If there are any unsynced documents, try synchronizing them and see if you get the same error. If synchronization fails, you could try dropping and recreating the domain(s). 

To drop and recreate a search domain follow these steps. 

1. Go to "Search Domains" window in IEE.

2. RMB on the relevant search domain and select "Show Details...". This will direct you to the detail view of the search domain. 

3. RMB on the detail view and select "Drop Search Index".

This will drop the search domain. Refresh the window to see that it is dropped. 

4. RMB and select “Schedule Domain Activation”. 

5. Click on “Enable Schedule” link. This will direct you to Task Schedule window. 

6. RMB and select “Run”. 

7. Click “View background jobs for this task”. This will show the background job created for this. 

8. RMB on the Background job and execute if it isn’t already executing. 

9. Go through step 1 and 2 above again. Then click on "synchronized".

10. Go through steps 6, 7 and 8 above. 

After doing the above, go back to Search Domain detail window and see if the domain is activated and all the documents are properly synced. Refer to "Not Synchronized Documents" column for this. Value should be '0'. 
 

Thanks it works.