Sounds like a skin error. ML2 being a legacy type plugin has it's skin in devnz\gbpvr\skin. And while it will copy it's skin there, it needs supporting files as well. 1.2.13 removes this skin directory. Theres a thread by me in the community announcements with a zip file with a basic skin directory. Apply this and you should be ok.
The other thing it can sometimes be is there may need to be a MusicLibrary2 directory in the skin2 directory - this is somtimes used internally by gbpvr for verification of the skin.
AMD FM1 x4 A8-3870 Llano, Gigabyte GA-A75-D3H, 4 Gb DDR3 Ram, Seagate 500 Gb, Seagate 1500 Gb, HVR3000 x 2 (DVB-S), Nova-T 500 (DVB-T), USB-Uirt, SPDIF -> Yamaha RX-V540, ATI HD6550 (OnBoard) > Samsung LA46A650 TV (HDMI), Harmony Remote 525
Windows 7 Ultimate x64 SP1, NPVR 2.4.3, AC3Filter, 1 x Popcorn Hour A-100, 1 x AppleTV with Plex