If you reinstall VPOP3 it is possible that you may end up with two VPOP3 Status Monitor icons in the task tray. This doesn't mean that two copies of VPOP3 are running, just that two copies of the VPOP3 Status Monitor are running.
When you install VPOP3 it asks you whether you want the Status Monitor to run for all users, or only for the currently logged in user. Depending on the option you choose, VPOP3 will start the VPOP3 Status Monitor either from the current user's Startup group, or from the “All Users” Startup group. If you install VPOP3 twice and choose different options on the two installations, you can end up with the VPOP3 Status Monitor being started from both Startup groups.
To only have one VPOP3 Status Monitor running, you need to remove it from one of the Startup groups, by going to Start → Programs in Windows. Depending on your version of Windows there may be two separate Startup groups, or both might be merged. You need to remove the VPOP3 Status program from the appropriate Startup group. The changes will take effect when you next load Windows.
From XP onwards, Windows shows a 'merged' Startup group in the Start → All Programs menu. This means that it will only look as if one copy of the VPOP3 Status Monitor should be being started, and you can't easily manage both copies from there.
Before continuing, choose whether you want Status Monitor to start for all users, or just the logged in user.