ASUS21 should be the certificate ...... and you have to unhide the extensions for know filetypes in the PC .... (folder options)
AC86AA31_SLIC.rom filename is too long, it must be 8+3 digits. Try this repack: Jetway_AC86AA31_ASUS_SLIC_DYNAMIC.rar mediafire.com/?0ws838nldk0g3st Flash from DOS using Mod.bat file. Confirmed working by wantons.
Taking the advice From Ipmark, I rename AC86AA31_SLIC.rom to a shorter name like ASUSSLIC.rom, then flash it again. Guess what! Everything works great now. Thank a lot!