Here
[[fileListArray objectAtIndex:i] objectAtIndex:0]
[[modifiedArray objectAtIndex:i] objectAtIndex:1]
[fileListArray objectAtIndex:i]
and [modifiedArray objectAtIndex:i]
are not NSArrays (I think they are both NSStrings).
You just need to remove the erroneous objectAtIndex:0
and objectAtIndex:1
messages.