\"Volume set to Transfer only\"??

I'm running 7.1 with an mbox on an iBook G4 and using an external LaCie drive. last night i was editing drums in a couple sessions, everything went smoothly. then today when i went to open ANY sessions on that same drive i got "this session is saved on a volume set to transfer only". which is weird because i'm pretty sure i didn't do anything to change it. then when i went to the details of the drive it says that i can Write and Read on it. so i'm not sure what the deal is. i put another file (not a PT session) on the drive and opened that fine.

Click the 'Window' menu, and select 'Workspace'. In the window that comes up, select the letter 'T' (for Transfer) next to your drive, and set it to 'R' (for Record). If it won't let you change it, delete the Digidesign databases folder from the drive, restart, and try the process again. If it still fails, delete the Digidesign databases folder from the drive once again (if it has been re-created), delete all Pro Tools preference files, restart, and try the process again. Good luck, onlyone-jc.

there we go. Thank you very much. I appreciate your taking the time to help.