people start downloading for hours but fails at the end. :(

[\dev\null]

dear folks,
i have been serving with the latest invision with the latest patch for 2 days now. even though i am behind a router by linksys, i can 'get' & 'send' files without tweaking any of my router's setting.
anyway, when people download huge files from me (>300mb for example), their downloads will get disconnected even though they are, for instance, 80% to completion. some of these people are frustated because they have beend downloading my files for 5-8 hours for example only to find out that their perfect download get disconnected for a reason i am not sure.
i have made sure that the the option "size guard" is disabled. by the way, this problem only arises when people are downloading huge files that take hours. small files less than 50k(which i set on the "instand-send" option to on) are successful. also, i am not running any firewall at the moment, only norton antivirus. no windows xp built-in firewall is run too.
any thoughts, advices, helps and etc are greatly appreciated.

sincerely,
\dev\null

[mustang03282]