Time Machine failure, read only

I've had an external storage device running as time machine for a year or so now, but have just started to get the following message

"Files can’t be copied onto the backup disk because it appears to be read-only."

I have not changed anything that I am ware of has anyone got any ideas?

Capacity of the drive was 999GB and seems to be 556GB available.

rgds
Chilts

That's odd, I also have been getting "Time Machine Failure" episodes for no reason that I can see! Unfortunately, I have not really paid attention to what the error message was. I seem to solve it by unplugging the external drive and re-plugging it back. Then, Time Machine sees it! I don't know why it just started doing this.

That's probably a sign that the directory or permissions have gotten corrupted. Try repairing the volume with Disk Utility as a first step, see if that helps.

Yes it might be permissions check out permissions on info on drive to see if you have read & Write permissions..