closing mdi child form causes System.ObjectDisposedException - vb.net

Question

i created a mdi database application. One child form has a datagridview. when clicking on a button on that form a new form opens with a pdfviewer(AxAcroPDF1) on it. This form shows a pdf document stored in the sql server database.
closing this form is done by Me.Close(). It closes it, but when i do it several times, opening that form and closing it, then at one point i get a
System.ObjectDisposedException which says Cannot access a disposed object and it isn't caught either in the try catch block.
It also says The application is in break mode. Your app has entered a break state, but there is no code to show because all threads where executing external code(typically system or framwork code)
Never experienced this kind of problem before.
Here is the code to launch the form with the pdf viewer
Private Sub btnShowDocument_Click(sender As Object, e As EventArgs) Handles btnShowDocument.Click
frmDocument = New frmShowDocumentatie
rowIndex = dgvData.CurrentRow.Index
FileName = dgvData.Item(6, rowIndex).Value
If FileName = "" Then
MessageBox.Show("Can't open documentation" & vbNewLine & "File doesn't exist", "Database Info", MessageBoxButtons.OK, MessageBoxIcon.Information)
Else
frmDocument.Show()
End If
End Sub
And here's the form that opens up then
Imports System.Data.SqlClient
Public Class frmShowDocumentatie
'local variables to get passed the public shared values from
'curent selected row index and document name in datagridview
Private iRow As Integer
Private fName As String
Private Sub frmShowDocumentatie_Load(sender As Object, e As EventArgs) Handles MyBase.Load
'sets the mdi parent
MdiParent = MDIParent1
'sets the text of the form to the filename of pdf bestand
Me.Text = "Document: " & getFilename()
'loads the pdf bestand, need the filepath which is provided by getfilepath function
AxAcroPDF1.src = GetFilePath()
'gets the values from the selected row index and corrsponding filename
iRow = frmDataView.rowIndex
fName = frmDataView.FileName
tsmiDocument.Text = "Document: " & getFilename()
End Sub
'function for getting the filename of selected pdf file in datagridview
Public Function getFilename() As String
fName = frmDataView.FileName
getFilename = fName
End Function
'gets the file path of selected pdf bestand
Function GetFilePath() As String
'Dim i As Integer = frmVerledenOverzicht.dgvData.CurrentRow.Index
'Dim filename As String = frmVerledenOverzicht.dgvData.Item(6, i).Value
Dim sFilePath As String
Dim buffer As Byte()
Using conn As New SqlConnection("Server=.\SQLEXPRESS;Initial Catalog=AndriesKamminga;Integrated Security=True;Pooling=False")
conn.Open()
Using cmd As New SqlCommand("Select Bestand From dbo.PaVerledenOverzicht WHERE Documentatie =" & "'" & getFilename() & "';", conn)
buffer = cmd.ExecuteScalar()
End Using
conn.Close()
End Using
sFilePath = System.IO.Path.GetTempFileName()
System.IO.File.Move(sFilePath, System.IO.Path.ChangeExtension(sFilePath, ".pdf"))
sFilePath = System.IO.Path.ChangeExtension(sFilePath, ".pdf")
System.IO.File.WriteAllBytes(sFilePath, buffer)
'returns the file path needed for AxAcroPDF1
GetFilePath = sFilePath
End Function
Private Sub tsmiSluiten_Click(sender As Object, e As EventArgs) Handles tsmiSluiten.Click
Try
Me.Close()
Catch ex As Exception
MessageBox.Show(ex.Message, "Database Info", MessageBoxButtons.OK, MessageBoxIcon.Error)
End Try
End Sub
End Class
anyone knows what's causing this exception and why is the program crashing instead of being caught in the try catch block
Am using visual studio community edition 2017