Catalog 'index file on the search server Search' error on WSS 3 Search service

Everything was running fine for a couple of months and then the following error started to appear on the index server every five minutes:

Event Type: Error
Event Source: Windows SharePoint Services 3 Search
Event Category: Gatherer
Event ID: 2424
Date: 27/09/2007
Time: 13:40:01
User: N/A
Computer: EP-SP-INDEX01
Description:
The update cannot be started because the content sources cannot be accessed. Fix the errors and try the update again.

Context: Application 'Search', Catalog 'index file on the search server Search'

There are lots of articles on this, one of them with a list of 15 suggestions to resolve the problem! However, I managed to find an article from Ivan Wilson at http://guru-web.blogspot.com/2007/08/wss-30-content-indexing-update-cannot.html that solved it for me (thanks, Ian). Ian says as follows:

"I fixed this by going to Central Administration – Operations – Services on Server. I selected the Windows SharePoint Services Search entry. I then changed the Service Account username and password to match the Content Access Account details. Click OK on the bottom of the page and wait five minutes."

"Once I saw that the error was no longer being logged I went back and set the Service Account back to its original username and password. Still no sign of the error. I also verified that WSS was indexing content again."

So that is exactly what I did. I had two service accounts - one called SP_WSS_SearchSVC and SP_WSS_SearchCA, so I entered the SVC account for both the service account AND content access account, restarted the service and it worked.

The only thing that differed from Ian's findings were that when I returned it back to having the SVC account as the service account and CA account as the content access account, the error reappeared straight away, except that it also reported a one-off error with trying to read the Central Administration site, as follows:

Event Type: Warning
Event Source: Windows SharePoint Services 3 Search
Event Category: Gatherer
Event ID: 2436
Date: 27/09/2007
Time: 13:50:01
User: N/A
Computer: EP-SP-INDEX01
Description:
The start address cannot be crawled.

Context: Application 'Search index file on the search server', Catalog 'Search'

Details:
(0x80131534)

Not sure why all this started (it may have been after some SQL maintenance plans were run), so it's probably something to do with permissions somewhere, but rather than spend an age trying to discover what it was, I ended up using the service account for both services and content access - There shouldn't be any security implications of doing this because both accounts are only Domain Users, with identical SQL permissions, and this is only for indexing the WSS help files anyway. The only difference is that the service account is being used to run the Windows service, which gives it slightly more permissions on the Index server itself.