Link to server lost & No such file or directory

On the upload, I drag and drop files from my location folders on my desktop to the destination folder on my server; but I noticed that the file size had been drastically reduced by the transfer. I checked the session log and it usually says either "Link to server lost" or "No such file or directory." Occasionally, the whole file I'm uploading does make it through. But most of the time, it does not. And the size of the resulting file fluctuates rather randomly. I'll drag and drop the file over, say, four to eight times before I get lucky and the file makes it through intact. Can anyone help me make my transfers more stable? It's killing me...