The error you get means that you attempt to connect to a local repository via file://
protocol but URL you enter either points to nowhere or you lack access permissions to the directory. So something is either wrong with the URL or with your access permissions. Here are the general troubleshooting steps:
Make sure to use the same URL in VisualSVN as you use in TortoiseSVN,
Make sure that you run Visual Studio and TortoiseSVN under the same user account. Network folders are mapped on per-user basis so if you run Visual Studio under another account, the
F:\
mapped network drive is unavailable. In fact, I guess that you run Visual Studio underAdministrator
and TortoiseSVN under some other user account.