Displaying Container Field Contents on Lasso page

I'd like to include an image file stored in a FileMaker container field, 'schoolimage', in a FileMaker database, 'Schools' on the record detail page.

So, following the description in Omnipilot's language guide, I have created a file, 'schoolimage.lasso':

**********

[inline: -Database="Schools", -Table="Schools_online", -FindAll][Records][Var: 'Bytes' = (Database_FMContainer: 'schoolimage')]...[/Records][/inline]

[inline: -Database="Schools", -Table="Schools_online", -KeyValue=(Action_Param: 'ID'), -Search][File_Serve: (Database_FMContainer: 'schoolimage'), -File='schoolphoto.jpg', -Type='image/jpeg'][/inline]

**********

and then put an image link on the record detail page:

**********

<img src="schoolimage.lasso?ID=[KeyField_Value]" />

**********

But schoolimage.lasso always returns the error:

Error Message: Error: Field not found or enabled.

Error Code: -1

The field 'schoolimage' was added to the database after the snapshot was created but it was refreshed to include it.

Can anyone suggest the problem?

Thanks for your help.