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I've had this problem a lot.

I solve it by opening Disk Utility, unmounting the disk, and remounting it.

Then: Back up now.

Don't format the drive until the last resort.

Good Luck!

I'd write a script to open disk utility, select the BU drive, unmount, mount, quit Disk Utility, and close its window. BUT I don't know how to write scripts.

Can anyone help?
 
Disk Utility

Unmounting and remounting the time machine volume is a quick fix. I do not know what causes it.
 
Is anyone still having this problem? Ive tried rebooting, unmounting, mounting, etc... Nothing is working. I dont know what to do...

I have same problem, I just drag the external Hard drive icon to the trash and turn it off, then turn it on again and it works fine. I don't know the real solution and it's annoying but this works for me every time.
 
Worked for me after OS update to 10.5.8

I have same problem, I just drag the external Hard drive icon to the trash and turn it off, then turn it on again and it works fine. I don't know the real solution and it's annoying but this works for me every time.

Less than 10 minutes after permitting Apple to update Leopard to 10.5.8, I got the same "Time Machine Read Only" message. Tried this solution, told TM to "Back up now" and it worked.

I wonder how many other victims are using MacBooks that are loaded down with peripherals. I've got a full publishing workstation with three printers (multifunction, color Deskjet, Dymo label), scanner, 24-in monitor, a 250G FW and a 500G USB, keyboard and trackball on this 2G bus with a 160G internal. Might that have something to do with it?

The WD 500G USB, by the way, has a twin living in my safe deposit box. They trade places every Friday. Even if my house blows up, I still have a business (assuming I'm not in the house when it blows up).
 
started appearing on leopard & snow leopard

I got his "read-only" errors both on my snow leopard machine and my father's leopard machine, both with no other peripherals except keyboard & mouse and the occasional memory stick. An unmount and power cycle on the external disks worked fine, but that is only a work-around. It smells like a bug introduced recently in an OS upgrade. Anyone knows a solution? I am not going to reformat the drive with 2 years' worth of backups...
 
I was wondering if maybe it was something to do with multiple user accounts on the machine. I say this because the first time I saw that error message was when someone else (on a Standard account) was logged in.

Does anyone know how the permissions work on a Time Machine drive? As the computer administrator, I've got all my folders protected so only I can access the data. Would this be the same on the Time Machine?
 
When in doubt, reboot

This problem just happened to me, and not for the first time. Deleting a few of the oldest backups to free up some space didn't help.

What did work for me was just restarting my Mac. While it was restarting, I also powered off for a few seconds the external hard drive I back up to. After everything was up again, I chose Back Up Now from the Time Machine icon, and the backup ran successfully again.
 
problem solved for now

Hi all,

I had this problem happen to me a couple of days ago. Not only was my Lacie 1TB Rugged XL Hard Drive being reported by Time Machine as 'Read-Only', the icon was not even showing on the desktop once the drive was connected and switched on, and also the drive wasn't showing as an available disk in the Time Machine Prefs.

I could however see the disk in Disk Utility, and after seeing that my symptoms were exactly as others had described in this thread - I clicked Veirfy Disk.

DU informed me the disk was in need of repair, so I went ahead and clicked repair disk from the menu. After a few minutes, I was again informed that the disk could not be repaired and that I should back-up my files (how ironic) and erase the disk.

By this stage however, the disk had then reappeared on my desktop. I went back into the Time Machine Prefs, found the disk available once more, and at the time of writing I have successfully completed a back-up of 6.5GB of data.

Strange situation that I can't trace back to a particular incident, either with MacOSX or the drive. Let's just hope it stays this way. Will report back if it happens again.

Cheers
 
The same exact issue!

This just happened to me about 5 minutes ago. It has also happened to me about a month ago and I had to reformat my backup drive.
...
What's weird is that if you do GetInfo you get

myusername - read/write
(uknown) - read/write
everyone - read only

Exactly the same thing happend to me BUT ON LION!!! And no issue when I was on sLeo!

After a month on Lion it makes me feel like Vista did ones... So many bugs. I feel like I'm in trap. :(
 
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Has anyone found a solution to this?
I have an external USB3 3TB HDD this is happening to.
 
Same Read Only Issue on 2TB WD drive

Copying files off drive painfully slow but what I am doing is...

Using a data recovery tool to "recover" the files. then I use that tool to "recover" to another drive. Doing it in Finder gives you a "file is locked" and copy cannot continue. My thinking is with "recover" the files are unlocked and hence copy can take place (although it is very slow for me).

I am trying to copy about 500GB of media (iTunes and iPhoto), I can lose the Movies as I can re-rip those.

Rippey
 
This happens to clients of mine on a lot of occasions, usually its because time capsule / time machine sparsebundles get too big and corrupt themselves, then they cannot be deleted or removed without force. I would obviously suggest you try all the above suggestions first, but if you have no luck - this is my solution:

If you can, start a new TC / TM backup on a fresh drive or on the same drive. Wait around two to three weeks so you have a healthy amount of backups to allow you to delete the old backups.

Navigate onto the TC or HDD where the time machine bundles are located. You should have your new one (check last changed date) and old one. Then run a force delete of the old one using terminal:

sudo rm -fr dragtheoldbundlehere

Hit enter, put your password in and wait around 10 - 20 mins depending on the size of the file.

This is a last resort fix, but it works. Use wisely and be careful with rm -fr!

In future, I suggest using alternative backups with your Time Machine backups. Don't rely on one backup source. Online backup is a good option too these days, so keep your data backed up online and locally (2 separate copies)..

Good luck!
 
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