Created Issue: Having problems using CreateWeb [10114]

Hi, I'm trying to use CreateWeb to create a sub site. Whatever I try I getting the error message:

"Value cannot be null. Parameter name url"

I've tried it with and without the webURL parameter. I've double checked the TemplateName and URL params

any help would be appreciated.

Thanks

the Code i'm using is

$().SPServices({
operation: "CreateWeb",
urlType: URL,
titleType: Title,
descriptionType: " ",
templateNameType: TemplateName,
languageType: 1033,
languageSpecifiedType: true,
localeType: 1033,
localeSpecifiedType: true,
collationLocaleType: 1033,
collationLocaleSpecifiedType: true,
uniquePermissionsType: false,
uniquePermissionsSpecifiedType: false,
anonymousType: false,
anonymousSpecifiedType: false,
presenceType: false,
presenceSpecifiedType: false,
async: false,
completefunc: function (xData, Status) {
alert(xData.responseText)
}