Xcode not letting me open a specific project
Open terminal and type

sudo chmod -R 777 /path/to/project_folder


NOTE: the capital R in the command above. Obviously change the path to your project folder to what it actually is.

If that command works without error,  but you still cannot open the project, then it isn't in fact a permissions problem but another bug in XCode.

You're not the first person to report this error however. Hopefully the above sorts it out for you.  Let me know.