v2.1.8 run error

I got this error when using v2.1.8

[Critical] Unhandled Exception
[Critical]
Object reference not set to an instance of an object.
[Critical]
at WGconsole.Program.ConsoleApplication(String[] args)
at WGconsole.Program.Main(String[] args)

Is this error because files are on FTP server and need this:
url_index.headers {credentials=username,password}

With version V2.1.5 everything is OK (i have W10)

Debian 9 x64
Mono JIT compiler version 5.18.1.0

Unhandled Exception:
System.BadImageFormatException: Invalid method header local vars signature token 0x 902523
File name: 'WebGrab+Plus'
[ERROR] FATAL UNHANDLED EXCEPTION: System.BadImageFormatException: Invalid method header local vars signature token 0x 902523
File name: 'WebGrab+Plus'