Background: To my knowledge, outside of upgrading to 1.1.3 last week, no changes have been made to the file structure in the past week or so (when I last recall it working) and we have not added any new addons.
Has anyone seen this or know how to resolve the issue?
That's the first place I went to look as getting a bit more detail is always worth while when troubleshooting. Unfortunately, there is no entry in the Server Error Log pertaining to this. Our last error was on 6/14 and this particular error was brought to our attention last night and verified in person today.
Quick update: I disabled all the addons on our site and we still experienced the exact same issue. Users are still not able to register new accounts and we still get the same error message as listed above.
Yup, that fixed it for us. When I checked the file structure, for some reason Uri.php was a 0kb file. I simply replaced it with what we had in our archive and we're good to go now. I don't know how that happened, but thanks for helping us track down the issue preventing people from registering!