It’s weird because it still opens the project, but I get this error when I try to open a project using the following syntax…

subl --project project-name

But after I close that dialog it opens just fine anyway. It’s a little confusing and annoying but livable for the time being, I’m hoping someone might now what the issue is.

I can’t replicate this issue unless I move/rename the project file, then, I’ll get that message as expected and a blank document will open. But, when the files is there, all works as expected with no error message.

I can confirm this behaviour.

Working on a Mac, using subl, I can create a project. I save the project file within the same folder (project folder).
When calling the project via ‘subl projectname.sublime-project’ or ‘subl --project projectname.sublime-project’ Sublime will open with the project, come up at the same time with the error message ‘Unable to read project …’. When I confirm the error message it comes back a second time with the same error message, and after confirming the second error message it will close Sublime.

While sublime is open and the error message not yet confirmed I can see the project open in Sublime.
I have the same issue on Ubuntu, just there Sublime does not close when confirming the error message.