sql stored procedure

hi.

I have this:

alter FUNCTION teste (@div nvarchar(10), @dep nvarchar(10), @sec nvarchar(10))
RETURNS @lista TABLE 
(
	mdnemp int primary key NOT NULL,
	mdnome nvarchar(50) NOT NULL,
	mvdivs nvarchar(50) NOT NULL,
	mvdept nvarchar(50) NOT NULL,
	mvsecc nvarchar(50) NOT NULL

)

as 
begin
	DECLARE @SelectStatement NVARCHAR(2000)
	
	if @div != ''
	begin
		set @SelectStatement = 'select mdnemp, mdnome, mvdivs, mvdept, mvsecc from colbrdor where  MVDIVS = '+ @div
	end
	if @dep != ''
	begin
		if @SelectStatement != ''
			set @SelectStatement = @SelectStatement + ' and MVDEPT = '+ @dep
		else
			set @SelectStatement = 'select mdnemp, mdnome, mvdivs, mvdept, mvsecc from colbrdor where  MVDEPT = '+ @dep
	end
	if @sec != ''
	begin
		if @SelectStatement != ''
			set @SelectStatement = @SelectStatement + ' and MVSECC = '+ @sec
		else
			set @SelectStatement = 'select mdnemp, mdnome, mvdivs, mvdept, mvsecc from colbrdor where MVSECC = '+ @sec
	end

	
	insert into @lista ( exec sp_Executesql @SelectStatement )
	return
end

i get and error in the line 

insert into @lista ( exec sp_Executesql @SelectStatement )

where is my problem?

Thank's in advance.