Feedburner feed error!

I found other posts like this also but i didn’t get any answers and they were also quite old.

So here is the problem: line 3, column 0: XML parsing error: <unknown>:3:0: xml declaration not at start of external entity
This is the error on feed validator.
I found out that i need to delete some empty lines in the beginning or in the end of some file. But which file?
Then i tried fix-rss-feed plugin for wordpress but it couldn’t too anything because it didn’t have permissions. And i don’t want to change every files permissions that it wants to modify.

So could anyone please tell me how can i fix it?