Expression evaluation error at function a!formLayout

Hi team,

i am refering appian application tutorial

i have interface 1 and interface 2, i wanna reuse  interface 2 into into interface 1...but shows error like this.....Could not display interface. Please check definition and inputs. Interface Definition: Expression evaluation error at function a!formLayout [line 4]: The contents field on a column layout cannot contain a form layout. Received a form layout at index 4.

INTERFACE 1

a!localVariables(
local!readOnly: ri!step="APPROVAL",
local!labelPosition: if(local!readOnly, "ADJACENT","ABOVE"),
a!formLayout(
label: if(local!readOnly, "Approve expense Report", "Submit Expense Report"),
contents: {
a!textField(
label: "Expense Item",
labelPosition: local!labelPosition,
value: ri!expenseItem,
saveInto: ri!expenseItem,
refreshAfter: "UNFOCUS",
required: not(local!readOnly),

validations: {}
),
a!dateField(
label: "Expense Date",
labelPosition: local!labelPosition,
value: ri!expenseDate,
saveInto: ri!expenseDate,
required: not(local!readOnly),

validations: {}
),
a!floatingPointField(
label: "Expense Amount",
labelPosition: local!labelPosition,
value: ri!expenseAmount,
saveInto: ri!expenseAmount,
refreshAfter: "UNFOCUS",
required: not(local!readOnly),
validations: {}
),

/*a!paragraphField(*/
/*label: "comments",*/
/*labelPosition: local!labelPosition,*/
/*value: ri!comments,*/
/*saveInto: ri!comments,*/
/*refreshAfter: "UNFOCUS",*/
/*height: "MEDIUM",*/
/*showWhen: ri!expenseAmount > 100,*/
/*required: not(local!readOnly),*/
/*readOnly: local!readOnly,*/
/*validations: {*/
/*if(len(ri!comments)<=100, null, "Your text has exceeded 100 characters")*/
/*}*/
/*),*/


rule!AT_enterComments(
showWhen: ri!expenseAmount > 100,
labelPosition: local!labelPosition,
readOnly: local!readOnly,
required: not(local!readOnly),
commentValue: ri!comments,
commentSaveInto: ri!comments
),



a!radioButtonField(
label: "Radio Buttons",
labelPosition: "COLLAPSED",
choiceLabels: {"Approve", "Reject"},
choiceValues: {true, false},
value: ri!approve,
saveInto: ri!approve,
showWhen: local!readOnly,
required: true,
choiceLayout: "STACKED",
validations: {}
)
},

buttons: a!buttonLayout(
primaryButtons: {
a!buttonWidget(
label: "Submit",
submit: true,
style: "PRIMARY"
)
},
secondaryButtons: {
a!buttonWidget(
label: "Cancel",
value: true,
saveInto: ri!cancel,
submit: true,
style: "NORMAL",
showWhen: not(local!readOnly),
validate: false
)
}
)
)
)

INTERFACE 2

a!formLayout(
label: "Form",
contents: {
a!paragraphField(
label: "Comments",
labelPosition: ri!labelPosition,
value: ri!commentValue,
saveInto: ri!commentSaveInto,
refreshAfter: "UNFOCUS",
height: "MEDIUM",
showWhen: ri!showWhen,
required: ri!required,
readOnly: ri!readOnly,
validations: if(len(ri!commentSaveInto)<=100, null, "Your text has exceeded 100 characters")

)
},
buttons: a!buttonLayout(
primaryButtons: {
a!buttonWidget(
label: "Submit",
submit: true,
style: "PRIMARY"
)
},
secondaryButtons: {
a!buttonWidget(
label: "Cancel",
value: true,
saveInto: ri!cancel,
submit: true,
style: "NORMAL",
validate: false
)
}
)
)