if you downloaded the A105 from the official LG site then it should be compressed with zip. If so, the chance that there will be 'random' corruption which you will not know about if you are using any decent archiver (WinAce, WinRAR, 7zip, WinZip, PKZip etc, not sure about Windows Zip folders) is very very small. The reason is because most archives including Zip store a checksum for each file (usually CRC32, e.g with Zip). The decompressor should (and with a decent archiver does) test the checksum of every single extracted file to make sure it matches the stored checksum. If it does not, it will tell you and you will know the file is corrupt. Therefore assuming you used a decent archiver, it is very unlikely to file is corrupt.
It is far more likely that there is a different problem. The fact that A104 works but A105 doesn't is a bit strange but it is easily possible LG updated their firmware writing tool. I would recommend you folllow their instructions exactly (read the readme) for example, make sure it is standalone as a master. I would also recommend you try your mobo chipset IDE controller not any Raid controller provided by an external chipset (whether on a card or on your board). Of course, if you are already doing this and following the instructions, maybe try an external chipset IDE controller (if you have one).
MTKflash will never work since it is for Mediatek chipsets!