You may see in ruTorrent a red arrow appear, and you may see an error such as:
Tracker Status: storage error:[file chunck write error:
Can not allocate memory]
This typically means you are running too many torrents for the RAM, or they are doing too much speed to cope. For example, having 50GB of torrents actively downloading and uploading at more than 5MB/s will show this error.
It is nothing to worry about however due to a bug in ruTorrent it will actually stay around until the download finishes. But, you can ignore it, and just be careful to run less torrents, or to pause some to let some finish.