Newbie question

Hello All

I am slowly working my way through Squeak and Seaside using "An Introduction to Seaside" and the Seaside examples as my learning guides.  I have come across an issue which I don't understand, and I am hoping someone could enlighten me as to what is going wrong.  The two methods below are called by MLHeadDataModelView>>renderContentOn:,  with MLHeadDataModelView>>renderCompanyTextInputOn: resulting in a MessageNotUnderstood: WARenderCanvas>>value: error.

The instance methods are:

MLHeadDataModelView>>renderCompanyTextInputOn: "This method generates the 'MessageNotUnderstood: WARenderCanvas>>value:' error"
self
        renderLabel: 'Company Name: '
        input: [
            html textInput;
            value: self headDataModelView companyName;
            callback: [:value | self headDataModelView companyName: value]]
        output: self headDataModelView companyName
        on: html.

MLHeadDataModelView>>renderEmployeeTextInputOn:
self
        renderLabel: 'Employee Name: '
        input: [
            html textInput setFocus;

            value: self headDataModelView employeeName;
            callback: [:value | self headDataModelView employeeName: value]]
        output: self headDataModelView employeeName
        on: html.

MLHeadDataModelView>>initialize
initialize
    super initialize.
   self headDataModelView: MLHeadDataModel new.

I don't get any error messages if I use the on:of: style, but not sure what exact difference or benefits are between the two.

MLHeadDataModelView>>renderCompanyTextInputOn:
renderCompanyTextInputOn: html
self
        renderLabel: 'Company Name: '
        input: [
            html textInput on: #companyName of: self headDataModelView]
        output: self headDataModelView companyName
        on: html.

MLHeadDataModelView>>renderEmployeeTextInputOn:
renderEmployeeTextInputOn: html
self
        renderLabel: 'Employee Name: '
        input: [
            html textInput on: #employeeName of: self headDataModelView]
        output: self headDataModelView employeeName
        on: html.

Thanks in advance for any feedback.

Regards
Adrian