edgavin, you have made things very clear. Thank you. You confirmed one thing to me. You are using packet writing to get the data on these CDs. I mentioned this before. Maybe I'll write it in capital letters so that other posters (not you) understand this. PACKET WRITING. That is not the same as "burning" a disk. Comments about "finalizing", "sessions" etc, do not apply. Great. Now we have cleared that out of the way.
Briefly, there are two common ways to get data onto a CD or DVD disk.
(1) Using a "burning" application (software program) such as Roxio Easy CD Creator, Nero Burning ROM, etc. With this setup, the data is transferred onto the disk in blocks called "sessions". You start off with a blank disk. You start up your burning app, tell it what files and folders you want to burn. Then you write the data to the disk in a "session". This may be a whole disk's worth of data, or less. If you finalize the disk, that's it. No more. You have a "single session" disk. If the session is smaller than the disk capacity, you have the choice of leaving the disk "open" so that one or more sessions can be added. This makes a "multi-session" disk. When you try to add a session that is bigger than the remaining capacity on the disk, the burning app will refuse and you then have to finalize or "close" the disk. Note that at ALL times during this process, the files that appear on the disk are read-only. They start that way and remain so, and are never otherwise. Even with an RW disk. To make an audio CD or video DVD you have to burn it. Disadvantages: perceived as cumbersome and complex by some computer users. Advantages: robust, easier to tailor the disk how you want it.
(2) Drive letter access. You can create, delete, copy, move, drag and drop files using Windows Explorer. This uses a technique called packet writing. After formatting the optical media it is then possible to write data in small packets, hence the name “packet writing.” The optical drive unit has to support the ability to write in small units, which all modern CD and DVD recording drives do. This way it is possible to save files onto optical media, as well as change, rename or delete them, or copy files separately onto the media. It is built into some versions of Windows where it is called Drive Letter Access ("DLA"). Also there are competing apps such as Nero InCD, and Roxio Drag-to-Disc (formerly Adaptec DirectCD). Files are read/write until an error occurs, at which time the app marks all files on the disk as read-only to protect your data. This is a simplified account, so please, no flames.
A handy page of information about DLA is here
http://en.wikipedia.org/wiki/Drive_Letter_AccessMany people have problems with DLA. These can be caused by bad disks, deteriorating drives, and software conflicts. You have been lucky for a while, it seems, but now you are having problems. I honestly think your best bet is to enrol in and post on a specialist forum such as CDFReaks. For example see here
http://club.cdfreaks.com/f34/data-formatted-dvd-rw-becomes-read-only-143021/