Purchased Tamron AFF004S700 SP 90MM F/2.8 DI Macro Lens for Sony Alpha
Camera. First put it on Sony A77. Auto focus fine for about 20 shots,
then AF stopped working. Turned camera off & on, re-seated lens, AF
still didn't work. Put lens on A65. AF would not work. Turned AF off
and on, messed with miscellaneous things (don't remember what), AF
started working again. Took 22 pics, then AF stopped working. Tried all
previous actions but AF will now not work on either camera.

Does auto focus failure sound like faulty unit or could operator error
or inability be the cause?

Thanks for help.
Don