NativeCommandError - pbiviz package not created

I'm trying to make a custom visual but when I run the pbiviz package command, I get the error below.

Can anyone tell me what it means and how exactly I can correct it? 

node.exe : error Package wasn't created. 2 errors found
At C:\Users\....\pbiviz.ps1:24 char:5
+ & "node$exe" "$basedir/node_modules/powerbi-visuals-tools/bin/pb ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: ( error Package... 2 errors found:String) [], RemoteException
+ FullyQualifiedErrorId : NativeCommandError

warn Please, make sure that the visual source code matches to requirements of certification:

Thanks!