Altiverb scans the impulse responses (IR) folder upon startup and then it writes a cache file. The next time Altiverb does not have to scan the entire IR folder, because it can read the cache file.
When you get the storage plist error Altiverb somehow cannot read or write the cache files.
I recommend you to delete the two cache files from your impulse responses folder (default location: C:\Program Files\Audio Ease\Altiverb 6\Impulse Responses) :
Then please right click on your impulse responses folder and hit properties. Then please make sure your user and the admin user can read&write in this folder and hit apply to all enclosed items.
Then run you host application (DAW) again. If this did not work, try re-installing Altiverb 6 but right click the installer icon and choose to 'run as admin'. Also run your DAW as admin, then this should work.