VB.NET - System.AccessViolationException: 'Attempted to read or write protected memory...' Occurs sporadically when using autoCompleteSource - vb.net

Question

System.AccessViolationException: 'Attempted to read or write protected memory. This is often an indication that other memory is corrupt.'
I started getting this exception after trying to implement AutoComplete into one of my text boxes. It seems to occur somewhat sporadically? It often occurs when trying to use AutoComplete within a couple seconds of loading it's panel but has occured upwards of 5/6 seconds afterwards too. Additionally if it doesn't occur, the AutoComplete can be used endlessly without crashing.
I've had the same error occur on two different machines so I'm really unsure of what could be causing this and would be endlessly grateful if someone could point me in the right direction!
I've tried to strip out all the parts that definitely aren't causing it to save space.
This code runs first:
Private Sub btnManagerEditItem_Click(sender As Object, e As EventArgs) Handles btnManagerEditItem.Click
refreshEditItemsScreen(False) ' clears all on screen data and repopulates DataGrid
txtManagerEditItemsSearchName.AutoCompleteMode = AutoCompleteMode.SuggestAppend
txtManagerEditItemsSearchName.AutoCompleteSource = AutoCompleteSource.CustomSource
End Sub
Private Sub refreshEditItemsScreen(refreshDatabase As Boolean)
dtgrdManagerEditItems.Rows.Clear() ' DataGridView displays items to user.
If refreshDatabase Then
updateItemDatabase() ' reads the database from file and updates _itemDatabase with it
End If
For Each entry In _itemDatabase ' Global variable holding the database
dtgrdManagerEditItems.Rows.Add(entry.Name, entry.Price.ToString("c"), entry.UniqueID, getStaffDictionary(entry.StaffID))
Next
End Sub
Private Sub updateItemDatabase()
_itemDatabase = readItemDatabaseFromFile()
End Sub
Private Function readItemDatabaseFromFile() As List(Of Item)
Dim pathtofile As String = IO.Path.Combine(My.Application.Info.DirectoryPath.Substring(0, My.Application.Info.DirectoryPath.Length - 21), "Item Database.xml")
Dim itemDatabaseFromFile As New List(Of Item)
If System.IO.File.Exists(pathtofile) Then
Dim objStreamReader As New StreamReader(pathtofile)
Dim xsSerialize As New XmlSerializer(itemDatabaseFromFile.GetType)
itemDatabaseFromFile = xsSerialize.Deserialize(objStreamReader)
objStreamReader.Close()
End If
Return itemDatabaseFromFile
End Function
Then this code runs when you start typing in the AutoCorrect box:
Private Sub txtManagerEditItemsName_TextChanged(sender As Object, e As EventArgs) Handles txtManagerEditItemsSearchName.TextChanged
txtManagerEditItemsSearchName.AutoCompleteCustomSource = _autoCompleteSource
End Sub
_autoCompleteSource gets it's value when this code is ran on form load (updateItemDatabase() is also ran on form load):
Private Sub updateAutoCompleteSource()
' reads the id dictionary from file and adds it to the auto complete source
For Each Itm In readItemIDDictionaryFromFile().Keys
_autoCompleteSource.Add(Itm)
Next
End Sub
Private Function readItemIDDictionaryFromFile() As Dictionary(Of String, String)
Dim pathtofile As String = IO.Path.Combine(My.Application.Info.DirectoryPath.Substring(0, My.Application.Info.DirectoryPath.Length - 21), "ID Dictionary.txt")
Dim output As New Dictionary(Of String, String)
If File.Exists(pathtofile) Then
For Each line In IO.File.ReadAllLines(pathtofile)
Dim parts() As String = line.Split(",")
output.Add(parts(1), parts(0))
Next
Return output
End If
End Function
Sorry if some of this code was unnecessary to post, I'm pretty lost as to what's causing the error so I just posted everything that runs before it occurs that I think could be related to it.
Thank you