Aria 2 not working for some files

I am using aria2 on a router with openwrt.
For downloading some files , "could not open existing files' ' is shown in Aria2.
It seems it is no problem for others to download the same files.
I have tried to find if there is a solution , but there is nothing.
Does anyone have the same experience for that? If possible , please share your ideas.
Thank you

Sounds like a permission error.