I use Outlook 2010 version 14.0.6023.1000 (32-bit), part of Microsoft Office Click-to-Run version 14.0.5139.5005, to send and receive four POP3 mail accounts.
A couple of weeks ago (I wish I'd noted the exact date), Outlook stopped exhibiting one annoying behavior and began displaying another, much more annoying, behavior.
The annoyance that went away: If there was only one message in my in-box and I deleted that message, the message would disappear from the list of messages (the middle column), but would remain displayed in the Reading Pane. I had to click on another e-mail account, or go to Calendar or Contacts, then return to the original e-mail account to clear the Reading Pane display. That was a minor nuisance, but I was able to work around it.
The new annoyance that won't go away: Every few hours (the timing seems to be totally random), Outlook begins throwing up Send/Receive errors. When I display the details, the error message reads "Receiving 'reported error (0x800300FD): 'Unknown Error 0x800300FD.'"
When the Send/Receive errors pop up, clicking on one of the accounts, and sometimes on Calendar and Contacts, causes the following message to be displayed on a gray background in the Reading Pane: "The file c:\users\(username)\appdata\local\microsoft\outloo k\accountname.pst cannot be accessed because another workstation has modified it. Close and then restart all mail-enabled applications. You might need to restart your computer." The POP3 account that gives me the error on any one occurrence seems to be random.
What other workstation? This is a home PC. I have a WiFi network with another workstation and a laptop, but neither of the other PCs runs Outlook, and the Send/Receive errors occur whether or not either PC is running. The PC with the problem does not have anything running in the background that monitors file status (I'm thinking of backup programs like Carbonite). For backup, I use Cobian Backup, which does a batch backup once a day. In addition, as far as I'm aware nothing else, in terms of new programs being installed or given major updates, happened around the time these errors started appearing.
Outlook checks four different POP3 accounts every 5 minutes. The Send/Receive errors seem to occur with any of the four accounts, at random. Investigating the "unknown error" part of the problem, I saw claims that the PST file in question had been corrupted, and recommendations to use SCANPST.EXE to repair the file. I tried that, several times, but the Send/Receive errors continued to occur.
In fact, I'm convinced the PST files are not corrupt and never have been: When the Send/Receive errors pop up, the (temporary) solution is simply to shut down and restart Outlook. That has worked every time, but it's annoying to have to keep rebooting Outlook.
I also tried to resolve the problem by going to the Programs and Features control panel and doing a repair on Microsoft Office. The repair successfully completed, but it did nothing to resolve the problem.
Has anyone else been experiencing this problem? More importantly, does anyone have a suggestion as to how to make it stop?