Hi there,

My backup troubles are not over yet. I have 3 Macs to backup and to do so I connected WD 1TB MyBook external drive to Mac #1 via FireWire. I created 3 folders in that HD and using Backup software (Apple original) I setup various backups.
Strange things is that when Backup starts it gives me errors. I went to see what is going on and it says:
" You don't have permission to backup to the "Mac #1 Backups" folder on "My Book". select different folder or destination"

I did go to System preferences > Sharing and listed those folders as shared. Something else has to be done here and I don't know what. Even Mac #1 gets same message when Backup tries to do it's job. Maybe it is something with Time Machine because I have Time machine enabled on this Mac. Other Macs didn't recognize that drive as TM drive available

Thank you,
Zack

Try repairing your permissions on your Mac. Also, highlight the external drive's icon and do a "Get Info" (Command-I). You can adjust permissions in there.

If you're doing complete back-ups, I'd suggest a different route.

Use Disk Utility to partition the WD drive into several partitions. One for each machine, with the size of each partition 25% larger than the drive it is intended to back-up, and the rest as one partition used for storing misc. items. Then use a program like SuperDuper! to make a complete back-up of each machine to it's corresponding partition. (SuperDuper! is free for making complete back-ups or you can buy the pay for version that allows for timed incremental backups, and more, as well).

Tried what Bmer said and can't change permissions. Take a look at attached picture. There is small lock in right lower corner most likely preventing me from changing everyone to read/write (if that is what I need to do).
I'll try to find repairing permissions in Spotlight. I don't know where is that function in this moment.

Click on the little lock icon and enter your password.

I just did what you said and managed to change "Everyone" to Read/Write, however Backup still fails. If I go to set it up it repeats the story that I don't have permission to use that folder even that i can easily open it and see it in Finder.
I also opened same drive in Finder in Mac #2 and was able to read and write to that folder just for test. it looks like it doesn't like when Backup is trying to do the same?

You can have ownership problems moving a drive between systems where the users have been set up in different orders. It's best to follow the advice to have a separate partition for each machine's backup even though that won't use the drive as efficiently.