Using 20 April 2010 Objective-Basic.
Selecting Project -> New File (either one). Regardless of the character or characters entered I get the following alert:
File name contains invalid characters.
Allowed characters are a-z A-Z 0-9 _
This alert, for example, was begat by the character "F". I tried all uppercase, all lowercase, mixed alpha and numbers, all to no avail.
This occurred when using the 23 March 2010 version as well as the latest 20 April 2010 download. I don't understand why this problem hasn't been encountered by anyone else. My MacBook is configured for the United States Keyboard.