If a project is read only, it is not always detected when the project is opened but only when a write to the project directory is attempted. For instance, if the project is located in a subdirectory of Program Files this is likely to happen.
This only happens when msvcr71.dll has not been copied to the BlueJ installation. Because if it has been copied virtualisation will be enabled and you can actually write. That breaks BlueJ in other ways though, see ticket
The error that is reported by BlueJ depends on the write action that is attempted. If trying to create a new file you get a BlueJ Error dialog saying that: "The default skeleton for the class could not be generated. This may be because of configuration error in the setup of BlueJ, or because of file system access problems." Or if you edit a source file and try to save it the editor displays this: "Error in saving file!"
This is probably due to the new access control features of Vista.
We should detect this problem when the project is opened to avoid all these different and not very helpful error messages.