I wouldn’t bother trying to learn what that specific –8003 error means. The Mac can throw up all kinds of error codes and very few of them make sense (or have much published about them). Instead, just assume something’s mucked up and go from there.

We’ll start with general muckage. Launch Disk Utility (/Applications/Utilities), select your startup drive in the left side of the window, click the First Aid tab, and click Verify Disk. Disk Utility will perform a check of your startup volume looking for any obvious errors. If it finds any errors, boot from another volume (in Lion this can be the Recovery HD partition, in earlier versions of the Mac OS, boot from the latest OS X installer disc). Again, run Disk Utility from this new volume, select your regular startup volume, and click Repair Disk.

With luck, everything will be repaired, you’ll return to your startup drive, and be able to empty the trash. Without that luck, you may have to turn to a sterner utility such as Alsoft’s $100 .

You say that Disk Utility found no problems yet you still can’t empty the trash. If you like pushing buttons, return to Disk Utility, select your startup volume, choose First Aid, and click the Repair Permissions button. Any luck? I thought not.