I encountered error 50 when I was trying to empty the trash....
I did the following
• Unmounted all the drive to determine if the problem was on the boot drive or an external. My boot drive was ok ( trash was empty when only boot was mounted )
•Unmounted each drive ( I have 10 mounted at any given time ) until I discovered the problem drive
•I erased that drive ( I temporally moved those files to a blank drive ) then moved them back after the problem drive was erased/fixed.
•I know this is not a practical solution of everyone ... but it worked for my configuration