I have a Windows 7 Pro 64bit computer with a mapped drive to our server on the internet. I can successfully logon and transfer small files, however the large files eventually fail and pop up a message box say "There is a problem accessing Z:\. Make sure you are connected to the network and try again", clicking the Try Again button doesn't recover the transfer. I once got this error 0x80070057: The parameter is incorrect but usually I just get the message box mentioned before. I have tried doing a transfer with my anti-virus turned off, with no success. I have downloaded Network Monitor 3.4 to try and find what is causing the issue but every transfer I do with Network Monitor running, completes. The transfer to the server does work on my Windows XP Pro computer but if I run a virtual machine on the Windows 7 computer then the transfer fails. Any suggestions would be greatly appreciated.

The diffrence between XP and Win 7 here is the version of SMB. Win 7 uses SMB 2 and XP uses SMB1 Instead of disabling the AV , can you please try to uninstall it Completely and see if that works. Also what AV software you are using? If it is SEP please upgrade to the latest version. There is known issue of SEP with SMB 2