error CS1061: Type `UnityEngine.WWWForm' does not contain a definition for `error' and no extension method `error' of type `UnityEngine.WWWForm' could be found. Are you missing an assembly reference?

trying to make a very simple “Unlock” character form…

	IEnumerator UnlockThis (){
		WWWForm UnlockForm = new WWWForm(UnlockShipURL);
		UnlockForm.AddField ("username", username);
		UnlockForm.AddField ("shiptounlock", ShipTOunlock);
		if (UnlockForm.error == null) {
			// REFRESH LOGIN.....

You have to make WWW call like this

WWW download = new WWW(url,form);
yield return download;
if(download.error == null){