I use tor-arm to manage my relay, at startup the following messages appear:

...

That issue certainly indicates that you lack permission to write to '/home/username/.arm' or a file in it. Unfortunately my only suggestion is to double check the permissions again.

Arm is telling you about this at the 'NOTICE' level because it's not really an error. Being unable to write the config descriptions simply means that the startup time will be a little longer (it's failing to cache some data). As for the message about insufficient uptime, that's perfectly normal.

Cheers! -Damian