FTP download files using WIP

I use Q2686 (Wip Soft v301 on Open AT OS v421) and MCU to develop an TCP/IP system. I need to download file with 18142B size.

THE command is:
-> AT+WOPEN=1
<- OK
-> AT+WIPCFG=1
<- OK
-> AT+WIPBR=1,6
<- OK
-> AT+WIPBR=2,6,0,""
<- OK
-> AT+WIPBR=2,6,1,""
<- OK
-> AT+WIPBR=2,6,11,“private.vpn”
<- OK
-> AT+WIPBR=4,6,0
<- OK
-> AT+WIPCREATE=4,1,“192.168.17.6”,21,“bblogin”,“bbpsswd”
<- OK
-> AT+WIPFILE=4,1,1,"./download/list.bat
<- OK
<- CONNECT

DCD is 0.
Receiving data (exc. ETX char., data are text) with flow control.
DCD is 1 after interval cca 3sec since CONNECT.
Link is quiet and modem does’t react to any command after receiving 15334B (always).
When transferring binary files (with ETX chars) this problem occurs when smaller files are transferred.

Where the problem could be?