If a resource was once able to enter time against your project but is no longer able to, one of three things might have happened:
In this case, an error will display at the top of the user’s timesheet when they save it.
Change the project status to In Progress to allow entry of time against it.
Ensure the Allow Time Entry against Task Only option is disabled for the project.
In this case, no error will display to the user’s timesheet, but the project won’t be available to add in the task selection field.
Add the resource to the project to allow entry of time against it.