Errors and Status Messages
FILE CHUNK ERROR / STORAGE ERROR: CANNOT ALLOCATE MEMORY
When you get that error, it means rTorrent is running out of available RAM to download to, and is moving data out of RAM and onto the disk. It doesn't usually happen with audio torrents since those are relatively small in size.
If you just let it keep running, it will work fine, downloading data to the disk, which is a little slower. It will finish downloading, and then it will look like it's hashing, but what it's actually doing is putting the pieces back together.
COULD NOT PARSE BENCODED DATA
This message is rTorrent's way of saying that there is a communication problem with the tracker. Just leave it be, and once the communication resumes, the error will go away. You may also go check with your tracker, to see if they are having issues.
TRIED ALL TRACKERS
From the developer himself:
It means it didn't manage to connect to any trackers. This can happen when libtorrent automatically requests more peers.