WL500gx-1.9.2.7-10.trx is intended for wl500g deluxe. I think Oleg was writing somewhen that on the asian market asus also supplied wl500gx ( I found such page: http://oleg.wl500g.info/devices.html ) which is another name of wl520g. There is no support of wl520g in Oleg's firmwares (wl520gU and wl520gC are completely different models). I guess that's your case. I think your one should be 3-4 years old.