StringBuilder error (Chunk Length)

Question

I created a program to keep several folders in sync with their backups. The testing and copying is done with a background worker which reads a list of the files in the "original" folder, looks for the same file in the backup and skips if it is
there or else copies it. It has been working just fine for months but suddenly I am seeing this error:
{"Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: chunkLength"}
   at System.Text.StringBuilder.ToString()
   at FileSynch.Form1.BGW_Copy_ProgressChanged(Object sender, ProgressChangedEventArgs e)
   at System.ComponentModel.BackgroundWorker.OnProgressChanged(ProgressChangedEventArgs e)
   at System.ComponentModel.BackgroundWorker.ProgressReporter(Object arg)
the line of code that throws the error is : TxtResults.AppendText(SB.ToString)
I tried setting the StringBuilder with the Int32,Int32 overload to a high value, which did not help. I tried synclock which didn't help. I haven't any idea if the chunk_length can be changed, nothing I find says it can.  Here are some of the details
from one exception:
Actual SB.Length = 4492 (&H118C)
SB.Capacity = &H5E80
SB.m_chunk_length = &H118A
SB.m_chunk_chars {Length = 24192}
MaxChunkSize = &H1F40
MaxCapacity = &H7FFFFFFF
this is the backgroundworker code:
For Each filename As String In Filelist
Sourcename = Path.GetFullPath(filename).Replace(Source, "")
DestnName = Path.Combine(Destn, Sourcename.Remove(0, 1))
FilesScanned += 1
SB.Append(Now.ToLongTimeString & "-Checking " & Sourcename)
If BGW_Copy.CancellationPending Then
BGW_Copy.ReportProgress(-1) ' just reports "User Cancelled"
Exit Sub
End If
If File.Exists(DestnName) Then
SB.Append(" - Backup Exists")
FilesSkipped += 1
Else
Try
SW.Restart()
Directory.CreateDirectory(Path.GetDirectoryName(DestnName))
File.Copy(filename, DestnName, False)
SW.Stop()
FilesCopied += 1
FLength = My.Computer.FileSystem.GetFileInfo(filename).Length
BytesCopied += FLength
SB2.Append(filename & " " & FLength.ToString & " " & TotalBytes.ToString & vbNewLine)
SB.Append(" - Copied " & ShowFriendlyNumber(FLength) & " in " & ShowFriendlyTime(SW.ElapsedMilliseconds))
Catch ex As Exception
SB.Append(" - Copy Failed " & ex.Message)
End Try
End If
SB.Append(vbNewLine)
If FilesScanned Mod UpdateFreq = 0 Then
BGW_Copy.ReportProgress(FilesScanned)
SB.Clear() End If
If BGW_Copy.CancellationPending Then
BGW_Copy.ReportProgress(-1) ' this just reports "User Cancelled"
Exit Sub
End If
Next
Progress Changed Code (simplified):
TxtResults.AppendText(SB.ToString) ' error here
UpdateFreq comes from a NumericUpDown and defaults to 10
A typical line of output:
9:46:34 AM-Checking \My DVD.iso - Backup Exists
or this:
9:48:12 AM-Checking \My DVD.iso - Copied 2.77 GiB in 38.0 sec.

Answer 1

Read another thread over at
stackoverflow suggesting that you should pass stringbuilder.Tostring across threads instead of the stringbuilder itself... Have you tried this?
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