Who is eating the bandwidth?

Hi there.
I’ve two ADSL line from two ISPs. One of them is on 2 Mb/sec. When I try it directly, it’s working fine. Then I configed my 439G as it said here:
http://wiki.mikrotik.com/wiki/Load_Balancing_over_Multiple_Gateways
I set up a mangle rule just for 1 IP address and route it with that 2 Mb/sec modem. But when I try it, it just give about 512kb/sec. What is wrong here?
I set up a simple queue for that IP like this:
Max Limit: Unlimited, Unlimited
Limit at: Unlimited, Unlimited
Queue type: default-small, default-small
Priority: 1
But again, nothing has changed. What should I do? Please help me, I had to have the band dedicated to my boss for tomorrow.

Thanks