WLAN network file transfer DELAYYYYY......

I just switched to AVAST Free Antivirus (7.0.1474.765) from free Avira AntiVir.

When I try to send large files (40-100MB) to another computer through WLAN it always gets stuck at 5 seconds remaining and it takes like a minute to finish the transfer.

This is very annoying since I do such transfers all the time. It is caused by the File Syestem Shield. I never experienced such delays with AntiVir.
It’s the same on all my computers (all running Windows 7 x64) with standard Avast settings so I assume it’s not a bug? I can’t see how this could protect my system.