Yeah, you're right -- that error wasn't helpful. I'd check your Xenos documentation to find out what a 'return code 8' means.
In terms of permissions, it should simply be readable by the user trying to read them. If the user who runs arsload is 'archive', then you'll want the owner to be 'archive', with permissions like 400 (aka u=r or r-- --- ---). If the user who owns the file is different from the user who runs the loads, but they belong to the same group, then make sure the group ownership reflects that, and set the access to 440 (u=r g=r or r-- r-- ---).
Good luck!
-JD.