It seems like you are on a different fork,
in the current 1553366 chain block 1520998 is 915c0024afd7820a68c9c0c5cd5303314862410bd0d8792fe9959f890fac5db1

You can't get past 1520998 because in your version of blockchain it's different.

To sync to 1553366 you have to delete blk0001.dat and txleveldb dir (or better save them somewhere just in case) and re-download the whole blockchain from scratch.