Internet flash won't work because the server for the BIOS files has changed, as noted in the latest BIOS version, 2.90, that changes the address of the server to the new one. Internet flash won't work until you apply version 2.90.
Sorry but I must ask, did you unzip the BIOS download file before putting the resulting file on the USB flash drive?
Why the Windows method does not work, who knows? I would try clearing the CMOS/BIOS first, and then try using Instant Flash again, with the appropriate file on the USB drive. The filename of the BIOS file should be just like this, for version 2.90: Z77EXT42.90