Hi danldurall,
It sounds like Send is timing out--there have been some issues with Send uploading large files, and Adobe is working on that issue. In the meantime, you're welcome to use Adobe SendNow to send your files (log in at https://sendnow.acrobat.com/SignIn.html). You can use the same Adobe ID and password that you use to log in to Send.
Please let us know how it goes.
Best,
Sara