In vast majority of cases, such issues are a result of corrupted app preferences (which are preventing mInstaller from accessing its database).
To fix this and rebuild the database, please do the following:
1) make sure that you are using the latest version of mInstaller,
2) use the Activity Monitor.app to close mInstaller if it's still running in the background,
3) switch to Finder and go to your Applications folder,
4) press and hold the CMD+Option(Alt) keys and double-click mInstaller.app
5) delete the app's preferences (you will be asked for your administrator password - be sure to provide it, otherwise the process will fail) and try logging back in to the app.