Are you still here? ;) Make sure that you have MAG 250, not 254, 256, 322 etc.! The Portal option can be disabled by operator when making customized image for STB.
IMHO you should try flashing official Infomir public image: http://soft.infomir.com/mag250/release/0.2.18-r22
Download file Bootstrap_250 and rename it to Bootstrap and download imageupdate file. Create mag250 directory in root of your pendrive (I recommend 8 GB with FAT32) and put both files in it.
Do flashing by USB & Bootstrap in bootloader menu ! ! !
NOT by embedded portal ! ! !
If it won't work, you can try reseting STB to factory settings.
Remember that you do everything on your own responsibility ;)