I had no problems with 10 miners/about 4Ghash/s with server ip put in DMZ, read some logs, it could be memory failure, overheating cpu, bad NIC, bad NIC drivers, missconfigured router, lack of free space on c:
it always dies inside boost library, I've put a screenshot herehttps://bitcointalk.org/index.php?topic=51567.msg614525#msg614525
I can't find anything usefull inside log file, this is what it writes
Added time data, samples 194, offset +2 (+0 minutes)
version message: version 40000, blocks=154222
received getdata for: block 00000000000001175695
disconnecting node 184.108.40.206:49695
cancel: Operazione richiesta non supportata per il tipo di oggetto indicato
C:\Programmi\Bitcoin\bitcoin.exe in ThreadRPCServer()
It says "cancel: Required operation is not supported by object shown".
ps. No problems whatsoever with cpu, space on disk, network drivers.