We are using the WinSCP .NET library (which came with version 5.5.3) and it was working was great for us until couple of days ago when we starting getting these exceptions during file upload. The thing is the file does upload successfully by calling the putfiles method below. However, the subsequent call to check the transfer result throws an exception stating the file already exist. Exact text is "Press 'Delete" to delete the file and create new one instead of overwriting it".
var transferResult = session.PutFiles(localPathToUploadFile, remoteFilePath, false, transferOptions);
The thing is that these are brand new files and so there should be no existing files to update, plus the same code was working fine until a few days ago which leads to me believe there could be something on the server which could be triggering the behavior as well.
Is the transferResult.Check() doing more than just checking?