Error counting number of users logged into the same database

I have a function that counts the number of users logged into and Access 2003 front-end running on a server.  This code (originally supplied via an EE post) has been working for years, but this morning I went onto a site and got an Error number 13 (type mismatch) error.

I haven't changed anything on this code (that I am aware of), but am wondering why it might not work.

Any suggestions would be massively appreciated.

Public Function CountUsers() As Long

    Const USERROSTER_SCHEMA As String = "{947bb102-5d43-11d1-bdbf-00c04fb92675}"  ' User roster schema GUID
    Dim rstUserRoster As ADODB.Recordset  ' User roster recordset 
    Set rstUserRoster = CurrentProject.Connection.OpenSchema(adSchemaProviderSpecific, , USERROSTER_SCHEMA)

    Do Until rstUserRoster.EOF
        CountUsers = CountUsers + 1  ' Can't use RecordCount!
        rstUserRoster.MoveNext
    Loop

end function

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