Error: The search request was unable to connect to the Search Service

I had seen that sometimes when user is going to search something on site he get this error message: -
"The search request was unable to connect to the Search Service".
Why it is coming??? How it can be solved???

Is coming becuase of your web front end server is not able to search database. The must be either the user don't have permission to connect with database or Index server is not set for search. No issue we have some solutions by this we can get the results not the error message:-

Solution 1:-
Step 1
* Central Admin -> Application Management -> Office SharePoint Server Shared Services -> Create or Configure this farm's shared services
* Shared Services Provider (drop down) -> Edit Properties
* Edit Shared Services Provider -> Index Server: Verify the index server is set
Step 2
Single Server Farm
On the MOSS 2007 server:
* Start -> Run -> CMD -> stsadm.exe -o osearch -action stop
* Start -> Run -> CMD -> stsadm.exe -o osearch -action start -role queryindex

Hopefully your search will be start.

If not then try another solution:
Solution 2:-
1. Go to Run ->type inetmgr.
2. Open the application pools.
3. Select the application pool related to Shared Service.
4. Right click on it and select properties.
5. On Identity tab change the Identity from Network Service to Configurable with passing your User name(with your domain name) and password .
6. Go to run and iisreset.

Enjoy Search Results!!!
(If still not getting the results then check search services on the farm they are start or stop if stop then must start them)