As Peter told you this usually means that there are no rights under the user that the apache server runs to access the files. This depend on the mechanism you have used to upload the dolibarr source files. More often that not it is done with root access so files are later not accesible by the user that runs the application.
If you are using a hosting provider they usually have a way to automatially ‘fix’ permissions for your files making them accesible form the user the engine runs as.
As Peter told you this usually means that there are no rights under the user that the apache server runs to access the files. This depend on the mechanism you have used to upload the dolibarr source files. More often that not it is done with root access so files are later not accesible by the user that runs the application.
If you are using a hosting provider they usually have a way to automatically ‘fix’ permissions for your files making them accesible form the user the engine runs as.