Did you do the half and half methid? This will quickly isolate what the potentials could be, and perhaps you could then post the executables in here and we could make a guess.

My own thoughts - security software or a utility of some sort.

At work i get this with MS outlook now and again. Even though you close the program it doesnt shut down the software correctly and the exe is still running, until you force stop it

I have tried the half and half method. I experienced the shut down problem with both halves of startup items.

So do it the long way round
Start with nothing ticked and then add an item one at a time.
If one triggers the problem then untick it and carry on until you have all the items which cause the problem unticked and the ones which don't ticked.
The report back which ones are causing the problem

I am unable to untick the Avast! start up item. Could this be the problem item?

Very possibly - try uninstalling it and see if that fixes it.
If it does then a clean install of Avast may solve the problem

Unfortunately uninstalling Avast did not stop the problem.

Edited by deleted (Tue 24-Sep-13 19:11:42)