Hello, i get error after upload 4Gb data with .Net 4.5 UploadSessionAppendV2Async()

This code get error on method UploadSessionAppendV2Async after 4gb upload.

static async Task ChunkUpload(DropboxClient client, String path, FileStream stream, int chunkSize)
{
int numChunks = (int)Math.Ceiling((double)stream.Length / chunkSize);
byte[] buffer = new byte[chunkSize];
string sessionId = "";
for (int idx = 0; idx < numChunks; idx++)
{
int bytesRead = stream.Read(buffer, 0, chunkSize);
using (var memStream = new MemoryStream(buffer, 0, bytesRead))
{
if (idx == 0)
{
var result = await client.Files.UploadSessionStartAsync(false, memStream);
sessionId = result.SessionId;
}
else
{
var cursor = new UploadSessionCursor(sessionId, (ulong)((uint)chunkSize * (uint)idx));
if (idx == numChunks - 1)
{
FileMetadata fileMetadata = await client.Files.UploadSessionFinishAsync(cursor, new CommitInfo(path), memStream);
}
else
{
await client.Files.UploadSessionAppendV2Async(cursor, false, memStream);
}
}
}
}
}