Could not create 1 connection in allotted time

[linup2011]

Could not create 1 connection in allotted time when run tcpkali, the command is as follows:

tcpkali --latency-connect -r 400 -em 'GET / HTTP/1.0\r\n\r\n' 1.1.1.40:80

and tool on the other side is nginx (1.1.1.40:80)

I checked that packets are sent on nginx, but I don't know why connection can't be created on tcpkali.
do you known the reason?

[root@dell-per730-41 tcpkali]# tcpkali --latency-connect -r 400 -em 'GET / HTTP/1.0\r\n\r\n' 1.1.1.40:80
Destination: [1.1.1.40]:80
Interface p4p1 address [1.1.1.41]:0
Using interface p4p1 to connect to [1.1.1.40]:80
Could not create 1 connection in allotted time (10s)

[linup2011]

and when request rate is lower, the connection can be created:

[root@dell-per730-41 tcpkali]# tcpkali --latency-connect -r 100 -em 'GET / HTTP/1.0\r\n\r\n' 1.1.1.40:80
Destination: [1.1.1.40]:80
Interface p4p1 address [1.1.1.41]:0
Using interface p4p1 to connect to [1.1.1.40]:80
Ramped up to 1 connections.
Total data sent: 8.7 KiB (8910 bytes)
Total data received: 2.0 MiB (2124045 bytes)
Bandwidth per channel: 1.706⇅ Mbps (213.2 kBps)
Aggregate bandwidth: 1.699↓, 0.007↑ Mbps
Packet rate estimate: 165.9↓, 49.5↑ (2↓, 1↑ TCP MSS/op)
TCP connect latency at percentiles: 0.1/0.1/0.1 ms (95/99/99.5%)
Test duration: 10.0038 s.