can only be indexed into using square brackets or the index function

Hi,

I am new to Appian and I am trying using a rule object as grid data source. but getting below error 

Could not display interface. Please check definition and inputs. Interface Definition: Expression evaluation error at function a!gridField [line 2]: A grid component [label="Read-only Grid"] has an invalid value for "columns". A grid column [label="Vehicleid"] has encountered an error. Expression evaluation error: AX TestVehicle can only be indexed into using square brackets or the index function

This is written in the interface 

{
a!gridField(
label: "Read-only Grid",
labelPosition: "ABOVE",
data: rule!AX_SearchVehicles(),
columns: {
a!gridColumn(
label: "Vehicleid",
sortField: "vehicleid",
value: fv!row.vehicleid
),
a!gridColumn(
label: "Vehiclemake",
sortField: "vehiclemake",
value: fv!row.vehiclemake
),
a!gridColumn(
label: "Vehiclemodel",
sortField: "vehiclemodel",
value: fv!row.vehiclemodel
),
a!gridColumn(
label: "Vehiclecolor",
sortField: "vehiclecolor",
value: fv!row.vehiclecolor
),
a!gridColumn(
label: "Vehiclecondition",
sortField: "vehiclecondition",
value: fv!row.vehiclecondition
),
a!gridColumn(
label: "Vehiclestatus",
sortField: "vehiclestatus",
value: fv!row.vehiclestatus
),
a!gridColumn(
label: "Vehiclecategory",
sortField: "vehiclecategory",
value: fv!row.vehiclecategory
)
},
validations: {}
)
}

------------------------------------------

This is what written behind AX_SearchVehicles()

a!queryRecordType(
recordType: 'recordType!{ae12c912-bb55-4de6-b097-819e20ae55ee}AX TestVehicle',
fields: {
'recordType!AX TestVehicle.fields.vehicleid',
'recordType!AX TestVehicle.fields.vehiclemake',
'recordType!AX TestVehicle.fields.vehiclemodel',
'recordType!AX TestVehicle.fields.vehiclecolor',
'recordType!AX TestVehicle.fields.vehiclecondition',
'recordType!AX TestVehicle.fields.vehiclestatus',
'recordType!AX TestVehicle.fields.vehiclecategory'
},


pagingInfo: a!pagingInfo(
startIndex: 1,
batchSize: 100
)
).data