None of these files helped, but I finally figured it out (thanks for nothing Apple!). Here is the benefit of my many hours of work. If you try the first option, please let me know if it worked. Now that my file is finally erased, I can't try it myself.
THE SITUATION: You have copied your Time Machine database “Backups.backupdb” to a new drive, and Time Machine is using it successfully. The old database is probably taking up a lot of room on the old drive. Mine was over 700 GB. You send it to the Trash, but you can’t empty the Trash (error code -8003). What do you do? Here is what I did:
FIRST, DO THIS: I spent a lot of time with the method below, and at the end I still had a 700+ MB file with no backups in it. I tried trashing and emptying the Trash but got the same -8003 error code. I did a “Get Info” on the Backups.backupdb file and saw that Sharing & Permissions was set to “system-Read” & Write and “everyone-Read only.” Click the lock, enter your password and change everyone to “Read & Write.” Close the Get Info box, send the file to the Trash and Empty the Trash. This worked. I suggest you try this FIRST. If the Trash empties, put your hands in the air, shout “Hallelujah” and be thankful you just save hours of work!
Now, if it doesn’t work that easily, I’ll take you step by step through what I did to get rid of the file. I would strongly recommend that you choose a time when you don’t need to use the computer for anything else. This will take hours, and might best be done overnight.
IMPORTANT: Before you begin, open Time Machine Preferences and turn OFF Time Machine!
1. With the Time Machine icon in the Dock, right click to “Browse Other Time Machine Disks”
2. Select the disk where the OLD Backups.backupdb file is located.
3. The front Time Machine window will be today, but the next layer back should be the last day the old database was used.
4. FROM THIS SCREEN, Click on your computer in the sidebar and Click on the Gear icon and select "Delete All Backups of ..." (If you select “Delete Backup” it will only delete this single backup.)
5. You will get a warning window to confirm you want to do this.
6. You will need to then enter your password in the next window.
7. Then you WAIT.
Time Machine begins be deleting the OLDEST backup first, then the next and the next. It’s hard to tell if anything is happening, but I discovered that during the deletion process, if you got to the oldest window you will see the file size deminish until the window is blank. Use the scroll arrow to move forward in time and you will see this happen again. The space available count at the bottom of the screen will slowly increase as well. Once you are comfortable that the deletion is happening, go to bed.
Good luck!