connection has been closed by server!

[ppserver]

Hi,
i run XAMPP server 1.8.3 for my windows server 2008 R2 and i'm very happy but my apache server logs errors some times and dont allow me to download my files from the server.
IDM error message:
cannot download the file... connection has been closed by server.

apache error log:
[Sat Oct 26 23:35:56.573608 2013] [auth_basic:error] [pid 3520:tid 1532] [client 217.xxxx:3746] AH01618: user amirxxx not found: /server/dl/Supernatural/S09/Supernatural.zip, referer: http://178.18.25.242/server/dl/Supernatural/S09/

please help me, how can i configure my apache to sole the problem?