deleting old back-ups in trash but not on Time Machine

Hi there

I'm stuck. I have a number of old back-ups that are sitting in my trash folder (on the external drive used for Time Machine) but are no longer in Time Machine itself so i can not delete them from there. When I try a secure empty of the trash folder these items remain and I get a code error 22, see image.

I'm running OS X Yosemite 10.01.2

Please help?