Why won't my trash empty or show that it is empty?

Question

HI!
I deleted a lot of files from my external drive then Trash deleted some of them but not all. I'm trying to Empty Securely Trash but it says: "The operation can’t be completed because you don’t have permission to access some of the items."
I tried to press the option key and then Empty Securely Trash but it didn't work.
When I log into my administration account and insert the external drive then it shows that Trash is empty but when I use my usual users account and insert the external drive then it shows that there are items in the trash but it won't let me Empty the Trash.
Otherwise both my admistration account trash and usual users account trash are both empty, Its only when I use my usual users account and insert external drive then it shows items in the Trash and won't let me Empty it.
So now I don't know if there are actually items in the Trash that I can't delete or the Trash is actually empty but for some reason it show that it is not and won't let me Empty it.
Tried restarting computer multiple times but still nothing.
Help!

Answer 1

Unfortunately don't have any other macs around here.
When I did Disk Utility then only Verify Disk and Repair Disk buttons are active. Verify Disk Permissions and Repair Disk Permissions buttons are not active at all. Don't know why is that. I assumed that they werent supposed to be active  with external harddrives as my other external harddrive which seems to be ok, when I mount it, then last 2 buttons I metioned also are not active. But if you say to use Repair Disk Permissions then something must be wrong with both of my external harddrives?
Anyway the external drive which Im concerned with right now  (the trash won't empty), when I did Verify Disk and Repair Disk then got this:
Verifying volume “MY PASSPORT”
** /dev/disk1s1
** Phase 1 - Preparing FAT
** Phase 2 - Checking Directories
** Phase 3 - Checking for Orphan Clusters
10158 files, 132201376 KiB free (4131293 clusters)
Verify and Repair volume “MY PASSPORT”
Error: Could not unmount disk
Verifying volume “MY PASSPORT”
** /dev/disk1s1
** Phase 1 - Preparing FAT
** Phase 2 - Checking Directories
** Phase 3 - Checking for Orphan Clusters
10156 files, 132201472 KiB free (4131296 clusters)
Verify and Repair volume “MY PASSPORT”
Error: Could not unmount disk