When a colleague tries to open attachments in her email (Outlook 2003 talking to an Exchange 2007 server) they take ages to open. The files are relatively small, all less than 1MB.
We've tried creating a new Windows profile for the user and tried creating new Outlook profiles, however that hasn't made any difference.
And we've tried accessing her account from someone else's PC, and the attachments open immediately there.
The only thing that might provide a clue is that Process Monitor shows Outlook on her PC trying to write the file to a folder within the user's "Temporary Internet Files" folder with FAST I/O DISALLOWED errors. Can't find a lot of useful information on that message online though.
What causes the FAST I/O DISALLOWED errors?
And would that make opening attachments so incredibly slow that opening a < 1MB file can take a matter of minutes?
UPDATE: Discovered that this isn't just an issue with Outlook. Other files being accessed over the network show the same FAST I/O DISALLOWED errors in Process Monitor. The problem is just more noticeable with Outlook, because although other applications take a while to open files it isn't a matter of minutes.
Best Answer
FAST I/O DISALLOWED just means that a process is trying to access file data and the system doesn't have that data cached.
It's documented quite extensively in the fourth edition of Windows Internals by Mark Russinovich and David Solomon.
So in relation to the problem we were having it makes sense to see these FAST I/O DISALLOWED errors because the data wouldn't likely be cached.
We never managed to work out exactly what was causing the issues with the attachments.