[Solved] SharePoint Search Internal server error exception

Users receive an error while performing a SharePoint search operation - Internal server error exception. This is the only message and rest is the standard Correlation ID information. But the Correlation ID is the most useful.

Upon reviewing the ULS logs using Correlation ID, the below error message is found. Check here - How to use Merge-SPlogfile to find logs based on Correlation ID error

SearchServiceApplication::Execute--Exception: 
System.Runtime.InteropServices.COMException (0x800703FA): 
Illegal operation attempted on a registry key that has been marked for deletion. 
(Exception from HRESULT: 0x800703FA) 
at System.Runtime.InteropServices.Marshal.
ThrowExceptionForHRInternal(Int32 errorCode, IntPtr errorInfo) 
at Microsoft.Office.Server.Search.Query.KeywordQueryInternal.Execute() 
at Microsoft.Office.Server.Search.Query.QueryInternal.Execute(QueryProperties properties) 
at Microsoft.Office.Server.Search.Administration.SearchServiceApplication.Execute(QueryProperties properties)

This issue does not seem to be related to permissions or configuration. Sometimes this looks intermittent. It seems some registry key has been marked for deletion but still has open handles or references.

Possibly something is wrong with the Search Query component. Now the query component can be hosted on multiple servers.

An easier option would be to restart related app pool, service on all SharePoint servers.

Follow the below steps to resolve this issue. If problem still persists, you may need to follow up with your Administrator.

1. From IIS - Restart (Stop-Start) the application pool for SecurityTokenService on all SharePoint FARM servers.
2. From Central Admin - Restart (Stop-Start) the Search Query and Site Settings Service on all SharePoint FARM servers hosting query component.
3. Perform an IISRESET on all SharePoint servers in FARM.