I was running a successful installation of IBM Unica Campaign on Windows 2003 VM. By some how I have to give a restart to the machine because it was halt. And I was with the following error.

Could not start the IBM Unica Campaign Listener service on Local Computer.

Error 183: Cannot create a file when that file already exists.

To resolve this issue you have to do following steps.
1. Make sure database is up and running. I was have Oracle database and checked it while connecting Sqlplus.
2. Start IBM WebSphere Application Server. Make sure Campaign, unica and dashboard applications are up and running in Enterprise Application section.

3. Navigate to <You Installation DIR>\Unica\Campaign\conf and delete unica_aclsnr.pid file. This is the file which is already there and listener is throwing error about it. We will delete it so that when we will start the Listener service, it will create a new file.
4. Right click on IBM Unica Campaign Listener service and click Start. It will work.