From yr log it seems that there is a conflict between the way you installed Ubuntu (as if yr existing hw context was BIOS-MBR) alongside a Windows 8 system that is UEFI-GPT based.
Your best solution, if yr install of Ubuntu is very recent and you have not invested hours and hours of configuration in it, would be to start again fresh from yr pre-installed Windows OS.
- get rid of Ubuntu
- make sure that Windows boots as before. If not, backup yr most recent Windows side data and restore Windows.
- boot from live Linux CD/DVD/USB drive and install Ubuntu anew, taking into consideration the fact that you are likely dealing with UEFI + Secure Boot + GPT on the preinstalled Windows' side. Many tutorials (e.g. [1],[2],[3]) can guide you through that type of installation.
You will certainly find help on AU to solve yr dual boot install trouble, but in my experience all what you need (and more in that department) is already available at ubuntuforums.org. The 3rd reference above is a good illustration of that.
HTH. Post yr feedback as a comment below if you have doubts or if you think my assumptions are misguided.