I'm not sure that the Shell command is the right choice here, since that will make the kix script wait until the vb script ends, which in this case is never. Try using Run instead. Also might need the full path to the vb script. Both of the below methods work fine for me.

 Code:
Run 'cscript.exe "' + @ScriptDir + '\test.vbs"'

 Code:
Run 'cscript.exe "C:\users\shane\desktop\test.vbs"'