Error 258 is a Windows 'Timeout' error. VPOP3 waits 30 minutes for the updater to complete its checks. It is very unlikely to take this long to check for and install any updates, so the usual reason for this problem is some security software blocking the updater from working.
Because the updater silently downloads files from the Internet and installs them, it is possible that security software will see this as suspicious behaviour. In this case, you can either disable the automatic updates (Settings -> Misc Settings -> turn off "Automatically Update VPOP3") or whitelist the updater program in your security software settings. The automatic updater is called "vpop3updateclient.exe" in the VPOP3 installation directory.
Note that it is rare that we release automatic updates at the moment, so disabling the automatic updater is unlikely to cause any problems.
Technical note - the updater will only download files from our website and will check SSL certificates on the downloaded files, so attacks such as DNS pollution or man-in-the-middle attacks will not be able to trick the updater to download unofficial files.