run with KL720 on VM but got error

Hi, I tried to build code on Virtual Machine Ubuntu 18.04.

cd kneron_plus/
mkdir build
cd build
cmake -DWITH_DFUT=ON ..
make -j

After building successfully, tried to run scan_devices.

ytl@ubuntu:~/kneron_plus_v2.3.0/kneron_plus/build/bin$ ./scan_devices 

scanning kneron devices ...
number of Kneron devices found: 1

listing devices infomation as follows:

[0] scan_index: '0'
[0] port ID: '4'
[0] product_id: '0x720' (KL720)
[0] USB link speed: 'Super-Speed'
[0] USB port path: '4-1'
[0] kn_number: '0xAB062D4C' 
[0] Connectable: 'True'
[0] Firmware: 'KDP2 Comp/F'

But when I ran generic_command, I got the error.

ytl@ubuntu:~/kneron_plus_v2.3.0/kneron_plus/build/bin$ ./generic_command -t KL720

[note - using default parameter values if no value is passed]
-target: [target platform] (KL520, KL720, KL630, KL730, KL830) = KL720 (default: KL520)
-sidx : [scan index] = default (specified scan index) (default: scan index of the first scanned Kneron device)
-port : [port id] = default (specified port id) (default: port ID of the first scanned Kneron device)
     Notice that scan index has higher priority than port id
-cmd  : [command type] (system-showSystemInfo, model-showModelInfo, reboot, shutdown) = default (default: system)
     Notice that the shutdown command is only supported by KL520 96 board

connect target: index '0', port ID '4'
connect device ... OK

getting system info error, error code: -7
PLUS_version: 2.3.0

disconnecting device ...

My question is why scan_devices shows no problem, but generic_command shows a connected error.

Could you please help me?

Thanks in advance!