Ad-Aware problems

I have been using the free program Ad-Aware to remove my spyware for a long time. A couple of weeks ago it suddenly stopped opening for me, told me it is being used by another user, that i am unable to use it.
I have tried dumping/deleting the program and reloading it without any sucess. Am I the only one having this problem with it? I have run my Spybot and Avast programs to see if there are any viruses in my system, and they say its clean. Any suggestions?