I recently implemented Fine Uploader and it's been mostly successful. A few users are however are not able to upload. They are all using modern browsers (IE10, FF and Chrome). One let me remotely access their machine and I was able to try it on both Chrome and FF.
I got the same error on both:
[10:45:28.330] "[FineUploader 3.8.0] Received response status 403 with body: <?xml version="1.0" encoding="UTF-8"?>
<Error><Code>AccessDenied</Code><Message>Invalid according to Policy: Policy expired.</Message><RequestId>--removed--</RequestId><HostId>--removed--</HostId></Error>"
Is it something with the timezone settings on their computer where it's generating an invalid policy?
The timezone settings will have no effect as times are UTC. However, if the time on the user's computer is not accurate (say, off by 5 or more minutes), then the policy will be expired, according to Amazon.
Fine Uploader sets an expiration date to 5 minutes (again, in UTC). The date used is generated in the browser, so your client machine's time will be used. If the client machine's clock is slow by 5 or more minutes, the policy will be seen as expired when Amazon handles it.
I'm fairly sure that the issue is due to a significant drift on your customer's machine clock. If you verify this, I suggest you instruct them to keep system clock synced with a time server.
Update: A new feature was added to Fine Uploader 5.5 that allows you to overcome extreme clock drift on user machines/browsers. See the clock drift section on the S3 feature page for more information.
来源：https://stackoverflow.com/questions/18520108/fine-uploader-getting-policy-expired-message-sending-to-s3-for-some