I've looked into it, but the problem wasn't what I expected.
What it looks like is a unmanaged error caused when the provided FTP account details doesn't have List permissions. This permission is required so that GameSave Manager can check if a file with the same filename already exists on the server (removing it so it can upload the new file).
Can you confirm that your FTP account has List permissions and try again?
That I'm afraid I cannot help with.
I performed this test within a Windows 10 virtual machine running FileZilla Server. The permission that I narrowed the issue down to was called List and was under the Directory permission group when configuring the FTP user account within FileZilla Server. No idea what this would be called in a Linux solution (which I'd imagine your provider uses).
Have you tried connecting to your FTP host through a dedicated FTP client (such as FileZilla)?
If there's an issue there, it might help you narrow down the issue (it'll likely give you an error code, which your host can use to debug the issue).
Does gs_mngr_3.exe have inbound and outbound permissions through your firewall?
It could be as simple as your firewall 'blocking' the data transfer and causing an issue similiar to what I managed to replicate via the List permission.