Doing a search using google, I find that nail.exe is apparently spyware.  

This forum section may be a good place to start.  http://delltalk.us.dell.com/supportforums/board?board.id=si_virus

By the way, I notice you are a new user.  Your question is a software issue, not a hardware issue and such should not have been posted in the General Hardware section of the forum.  Posting in the most correct section (and I know it can be confusing at times) helps to get issues resolved or resolved faster.   Also, all captial letters is considered "shouting" on many internet forums.

Sounds like you been hit by spyware.  Normally you will get this kind of messages when you been infected by the spyware and it is design to start everytime you start windows.  I suggest you run a spyware check again if you have already done so and go to Start>programs>startup and delete the shortcut linking to the nail.exe so you can stop getting that message everytime you start your computer.

Good luck