VB.Net datagridview event handler error

I have two datagridviews on my form.
Datagrid one loads some data.
The user clicks on a row and the second datagridview is supposed to display the records based on the information in the first datagridview.

this doesn't seem to work and I get an error that says Operation cannot be performed in this event handler.

Here is my code that loads the first data grid

 Sub fillUnmatched()
        Dim i As Integer = 0
        Dim cnUnmatched As New SqlConnection(connectionString)
        Dim sqlString As String = "SELECT orgAdvisorBenID, original_name, advisor_name, beneficial_name, institution_id " + _
                                  "FROM advisor_beneficial " + _
                                  "WHERE original_name IS NOT NULL AND institution_id IS NULL OR " + _
                                  "institution_id = 0 " + _
                                  "ORDER BY original_name"

        cnUnmatched.Open()

        Dim cmd As New SqlCommand(sqlString, cnUnmatched)
        Dim rdr As SqlDataReader = cmd.ExecuteReader
        While rdr.Read()
            frmUnMatched.dtgUnmatched.Rows.Add()
            frmUnMatched.dtgUnmatched.Rows(i).Cells("ID").Value = rdr("orgAdvisorBenID")
            frmUnMatched.dtgUnmatched.Rows(i).Cells("Title").Value = rdr("original_name")
            i += 1
        End While
        cnUnmatched.Close()
    End Sub

Here is my code that triggers the load of the second datagridview:

    Private Sub dtgUnmatched_CellContentClick(ByVal sender As System.Object, ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) Handles dtgUnmatched.CellContentClick, dtgSuggestions.RowEnter
        data.fillSuggestions(dtgUnmatched.Rows(e.RowIndex).Cells(0).Value)
    End Sub

Here is my code that fills the second datagrid - The error happens here when I add a row.

Sub fillSuggestions(ByVal ItemID As String)
        Dim i As Integer = 0
        Dim fillSuggestions As New SqlConnection(connectionString + ";Asynchronous Processing=true;MultipleActiveResultSets=true")
        Dim strSQLString As String = "SELECT UnMatchedID, orgAdvisorBenID, advisor, beneficial " + _
                                     " FROM suggestedMatches " + _
                                     " Where orgAdvisorBenID = '" + ItemID + "' " + _
                                     " ORDER BY advisor"

        frmUnMatched.dtgSuggestions.SuspendLayout()

        fillSuggestions.Open()


        Dim cmd As New SqlCommand(strSQLString, fillSuggestions)
        Dim rdr As SqlDataReader = cmd.ExecuteReader
        While rdr.Read()
            frmUnMatched.dtgSuggestions.Rows.Add()
            frmUnMatched.dtgSuggestions.Rows(i).Cells(0).Value = rdr("UnMatchedID")
            frmUnMatched.dtgSuggestions.Rows(i).Cells(1).Value = rdr("orgAdvisorBenID")
            frmUnMatched.dtgSuggestions.Rows(i).Cells(2).Value = rdr("advisor")
            frmUnMatched.dtgSuggestions.Rows(i).Cells(3).Value = rdr("beneficial")
            i = i + 1
        End While

        frmUnMatched.dtgSuggestions.ResumeLayout()
        fillSuggestions.Close()

    End Sub