MOSS 404 errors for some users on certain sites, sometimes - sharepoint

Question

Everything works fine for most accounts 100% of the time but here and there some users who are able to access a subsite fine one day are greeted with a standard 404 the next. This can last for an hour or two days, it's really inconsistent.
I check the iis logs and it says the status is also a 404 for these requests, nothing else looks unusual. Sharepoint logs have nothing for the timestamps either.
Correct me if I am wrong but if it was a permission issue an access denied message would be shown.
It is not the individual computer because when a user is having this problem and I can log in with their account and I also get the 404 error although I am on the exact site with another account in another browser at exactly the same time, and it works perfect.
Any suggestions would be greatly appreciated, I've done a fair amount of searching but can not find a similar situation or help anywhere.

Answer 1

Since the information is very strict at the moment, I will throw a few questions that might lead you towards the problem.
Are we on a loading balance setup? The intermittent 404 might be cause by one of the servers Web FrontEnds not correctly serving requests.
Are we running out of disk space in the SQL Server machine? This might cause it
Are the blogcache or site caches enabled? Some routines may break them
Do we have Anti-Virus on the server? (it HAS to be asked :p)
We get very high packet loss between the servers? (The error would be different though)
Something that might occur very often is when you have, say, custom code a DLL on the GAC or the bin folder, and since you could be on loading balance the second server does not have this DLL in its own GAC or BIN folder. Sharepoint usually raises 404s when assemblies are not found too, not only requests.

Answer 2

This seems like a longshot, but... could those SharePoint sites be throwing a 404 HttpException? It seems like you'd see that in the SharePoint logs, too, so it's even more unlikely.
At any rate, is your SharePoint logging level set to an appropriately verbose level to debug weird stuff like this?

Answer 3

Are people checking in & publishing master page changes when new CSS files and/or other includes (script files, etc.) are not yet published at all? I've seen this cause a 404 a few times when users forget to check before they publish.

Answer 4

I have had to write custom code within a SharePoint context and I had those 404 errors as well. The solution, in my case, was to ensure that the block of code executing had these 2 conditions met:
1) Run with elevated privileges, regardless of the fact that it is a 404 this was part of the solution.
2) web.AllowUnsafeUpdates = true; This line of code needed to be added even though it was wrapped within an elevated privileges block.
Once these were added the issue did not occur. This was happening on both load and non-load balanced environments.

Answer 5

This reminds me of a strange asp.net bug that I had a few months back.
It was caused by a patch that had been applied (to the framework if I remember correctly)
try downloading this Windows update list tool and have a look at what has changed since the problem started.
I concede that if there was a problem with a patch then its more likely that it would be a consistent error, but it's worth a look.

Answer 6

It was a permission issue, I had figured this out awhile back but basically a few accounts were not setup properly and could not load a fresh copy of the page, when someone else would hit it they would be able to view the cached page fine. Error was never thrown as a permission issue or access denied anywhere but this is what fixed the problem.