When you run "C:\Windows\System32\rundll32.exe vmnetui.dll VMNetUI_ShowStandalone" youre running rundll32.exe (which runs a dll file as an executable), and it's full path is included so it doesn't matter what folder youre running it from...except the next arguement youre passing to rundll32.exe is the file vmnetui.dll, which is located in the install location of VMWare Player. Because the full path isn't specified for the first arguement (vmnetui.dll), you must run this command from within the folder VMWare Player is installed in. The second arguement I believe is passed along to vmnetui.dll. The %1 mentioned in the error is a variable that represents the first arguement, "vmnetui.dll", and the second arguement, "VMNetUI_ShowStandalone", would be represented by %2. I'm not sure why the error isn't capable of showing you the value of %1 (vmnetui.dll) instead of the variable itself, but its typical of windows to make sure that error messages are not in any way informative.
Tip: one beautiful thing about windows is it is not case sensitive like linux.
To make a shortcut:
It's probably just as easy to make a shortcut to launch the program, that way you have it handy for future use. Right click somewhere on the desktop, go to "new", "shortcut", when it says type the location of this shortcut, paste in "C:\Windows\System32\rundll32.exe vmnetui.dll VMNetUI_ShowStandalone", click next, now name the shortcut something like "vmnetcfg" or whatever you like. Before you can use it, you need to tweak it a little. Right click on the shortcut, go to properties, click on the "shortcut" tab if it isnt already selected, and in the field titled "Start in:" enter the path vmware player is installed in, "c:\program files (x86)\vmware player". Apply, OK.
To run it from a command prompt:
This assumes you have installed vmware player in the default location on drive C. Do not include quotes when you type the commands.
go to start/run
type "cmd" and hit enter
type "cd\", enter
type "cd\program files (x86)\vmware player", enter
the prompt should reflect that you're now in this folder, if not the folder is wrong or mistyped.
now type "C:\Windows\System32\rundll32.exe vmnetui.dll VMNetUI_ShowStandalone"
P.S. It would be great if the nice folks at VMWare would take note of this post and perhaps in the future, create this shortcut for us at the time of installation. It's as if they're trying to hide it 
.