When you lost you CAroot password in ArcServe, you can reset it with these steps:

1. Open a command prompt on the server where you want to change/reset the caroot password.
2. In the command prompt browse to the drive where you have ARCServe installed (e.g. C:\Program Files\CA\...)
3. Once in the ARCServe folder type in the following: cstop. This will stop the ARCServe services that are running.
   
   
   
   
4. When all services are stopped open the Windows Explorer and browse to the folder: C:\Program Files\CA\BrightStor ARCserve Backup\Data\Discovery. Here you will find a folder that has the name of your server.
5. Rename this folder.
6. Back in the command prompt type in the following: cstart. This will start the ARCServe services that were stopped in item 4.
7. Still in the command prompt type in the following: Authsetup /p "password" where “password” is what you want the new password to be.
8. Close the command prompt and try to open ARCServe with the new password.

Source: Tek-Tips