inputMessage is null or not an object

[Mummy]

Hi there,

I fetched a dataset using web service and I attached it to a grid in this way:

ds = MainService.getFetchDS("GetPatients", "PatientAlias");
lstPatients.setDataSource(ds, lstPatients.getAllFields());
var criteria = {...};
lstPatients.fetchData(criteria, "UpdateEmptyMessages()", COProps);

and it all works fine.
Now, I've implemented deletion of records via service as well, but I want to delete the record from the grid manually (to avoid calling the service to fetch data again). When using lstPatients.removeSelectedData() I get the following error:
"inputMessage is null or not an object"
in isc_databindings.js file.
Is there a way of deleting the records manually without having to fetch the data again?

Thanx

Mummy