Create an ADODB connection inside a function VBA-ACCESS - ms-access

Question

I am trying to simplify my code, having a module which contains all DB connection functions in one Access, so this is what I've already done:
Module "DB"
Public Function connect() As String
Dim cn As ADODB.connection
cn.ConnectionString = "Provider=SQLOLEDB.1;Persist Security Info=False;Initial Catalog=system;Data Source=localhost; User Id= root;Password= root;"
connect = cn
End Function
Public Function sql(cn As String, query As String) As String
Dim rs As ADODB.Recordset
cn.Open
Set rs = cn.Execute(query)
cn.Close
sql = rs
End Function
Event when I click in a button
Private Sub btn_run_Click()
conexao = connect()
result = sql(conexao, "SELECT TOP 1* FROM MIS.MP_BASE_ACOES")
End Sub
Here is what my Access as an error:
Translating to en -> "Compilation error: The type defined by the user wasn't defined"
What am I doing wrong? Is that the correct way to define a connection function?
PS: There's no error in ConnectionString, I just changed some content because it is confidential.
Edit1: Following FunThomas, I really have forgotten to mark all the references like ActiveX from my project, but it still not working, now with this error:
"Uncompatible argument ByRef"

Answer 1

In general, you code has the following errors:
Wrong usage of functions (Public Function connect() As String)
The SQL function is not called
The object cn is of type string, and thus it does not have the Execute procedure.
Try this and try to assign the TestMe to a button. The idea to give the ConnectionString as a separate Function is a good one:
Option Explicit
Public Function ConnectionString() As String
ConnectionString = "Provider=SQLOLEDB; Data Source=1111111111; Database=ABC; User ID=NotSA; Password=NotTheSaPwd"
End Function
Public Sub TestMe()
Dim rs As ADODB.Recordset
Dim cn As ADODB.Connection
Set cn = New ADODB.Connection
Set rs = New ADODB.Recordset
cn.Open (ConnectionString)
rs.Open "SELECT * FROM TABLE", cn
Do While Not rs.EOF
Debug.Print rs!ColumnName
rs.MoveNext
Loop
End Sub

Answer 2

Currently you are passing a string when your function requires a connection object. Simply change parameter types accordingly:
Public Function sql(cn As ADODB.connection, query As String) As String
Dim rs As ADODB.Recordset
cn.Open
Set rs = cn.Execute(query)
cn.Close
sql = rs
End Function