Yeah. Silly me. I typed something in the box and they ungrayed. Older WinRAR's didn't have this behavior.
Regarding the absolute path. You need to type a drive letter.
<a name="HELPSFXOptGeneral">SFX options: General
This dialog is a part of the "Advanced SFX options" dialog and includes the following settings:
Path to extract
Set the default destination path for unpacked files. You may choose to create it in the user's "Program Files" folder, in the current folder or specify an absolute path here. In first two cases an entered path must not include the disk letter or leading backslash, in the third it must have one of them.
Corresponding SFX script command - Path