Double check the permissions of the directories forming the path to the configuration file (/home, /home/aria2, /home/aria2/.aria2) and be sure that the 'aria2' user can navigate them (ie, has read and execute permissions).
I have a partially downloaded file with aria2. Next to it, is a file with the same name end with .aria2.
I don't know the download link. I only have these two files. I want to know how could I resume download in this situation.