Password Cache is a storage where the program puts all found passwords. In some situations AOPR may ask for a "Cache password". This situation may occur if you set a password to protect your cache. You can learn more about Password Cache in the program documentation:

About Password Cache
Managing Password Cache

If you forgot your cache password or set it accidentally, you have to remove your cache file. Please do the following steps:

1. Close AOPR
2. Launch Windows Explorer and locate "c:\Program Data\Public\Elcomsoft\Advanced Office Password Recovery\Password Cache
3. Delete the "aopr.pwc" files