It's impossible to know from what you've told us, but what is clear is that the error is coming from a server. In other words, one of the uploads is failing because a file with the same name as the one you are trying to upload already exists on the server, and that file is locked. Why it is locked we can't know from the given information, so you'll need to study it a bit further.
I suggest firstly ensuring that your clients are not inadvertently uploading the same file to the same server at the same time. Once you've checked that then I'd investigate if some other client is doing it from somewhere else.
One common approach that can be helpful when there's a possibility of concurrent uploads of the same file is to upload the file using a temporary name and then rename once the upload is complete. In other words, if you want to upload a file called A.txt then upload it with a random name such as A-02389239.txt. Once the upload is complete then use the rename function to rename A-02389239.txt to A.txt. This reduces the time during which your client has a lock on the remote file, A.txt, from several seconds or even minutes, to just a few milliseconds, and thereby reduces the probability of a clash.
Of course, at a broader level you have to ask yourself if you really want to have several clients racing for file-locks and thereby overwriting each other. Perhaps there's larger design issue here.
- Hans (EnterpriseDT)
