I've been using Insync for a while, first on Windows 7 and now on Windows 10. Something I've noticed on both systems is that Insync consistently fails to upload files that are newly added to the Drive folder, giving the message "Can't upload - No read access".
If I click Retry, the file begins uploading immediately without fail. Or if I restart Insync it will also upload.
Since this behavior is so consistent, I have to assume that it has something to do with the way Insync accesses the file, specifically with how fast it tries to access it after its creation. I'm guessing that Windows still has sole access rights while the file is being created and if Insync tries to access it to upload it, Windows refuses and thus this message appears.
Most of the files I work with on a daily basis are small documents or audio files of a few dozen megabytes at most, so we aren't talking about files that take minutes for Windows to copy or save to the Drive.
My suggestion is to either add functionality to Insync that forces a retry every X number of seconds after failing to gain read access (with perhaps a capped limit of attempts to avoid spamming the file system unnecessarily, if that was an issue) or to increase the amount of time Insync waits before attempting to access a new file after it has been created.
Notably, I don't get these read access errors when modifying a file in the Drive, for instance when saving changes to a Word document. Insync seems to handle that just fine, and uploads the new version right away. It's only when a brand-new file has been created that it gets tripped up.
I know that I can just click Retry every time the error occurs, but I'd rather just be able to create files in the Drive folder and not have to open up Insync just so it tries to gain access to those files again -- I mean, that's kind of the point of Insync, to streamline this process.