I assume you have a file attached to the tax return? If so, It sounds like your file attachment is too big and the server is timing out before the entire file transmits. If it is a pdf file, you need to reduce the file size. This can be done in Adobe if you have a paid version or there are free websites where you can reduce a file size. Just be careful you use a trustworthy site. Research it first.
If you don't have a paid Adobe subscription, sometimes they offer 7 day free trials and you would just need to remember to cancel it before a charge.
Good luck!!
