Something's probably wrong with your internet connection. Or the internet in your area.
Transferring large files across the internet is hard. When you visit a website, any data you send, goes through dozens of connections before it gets to its destination. If anything goes wrong at any of those points, the connection will fail.
DistroKid makes transferring large files easy. The proprietary technology on DistroKid's upload form actually creates a direct-connection between your browser, and our file host (Amazon S3). This takes DistroKid's servers (and any points between your computer & ours) out of the equation.
Amazon S3 has servers all over the world. So wherever you're sitting, you're probably connected to an Amazon S3 server nearby. This usually makes DistroKid uploads extraordinarily fast and reliable.
If you get an error that says "your socket connection to the server was not read from or written to within the timeout period," it means that you started transferring a file, but then mid-transfer, the file host received no data from you for at least 20 seconds. Amazon S3 considers that a failure, and shuts down the connection.
What happened during those 20 seconds? Likely your computer (or your router, or the service in your neighborhood, or somewhere in the internet we don't control) isn't consistent. Try waiting and trying again later, or try your upload from another location.