With a TiVo remote that does not have separate Live and Guide buttons, try pressing TiVo button then Live button. After that, Live should bring up the Guide.
Hopefully that will fix the problem, however, I'm not sure why this is happening on a single tuner TiVo. Maybe the problem is related to DVD combo TiVos. A similar problem happens with dual tuner TiVos like the newer models, Series3, S2DT, and DirecTiVos, which come with a remote with separate Live and Guide buttons. On these models, Live does not bring up the Guide but rather swaps the tuner being viewed. But using an older TiVo remote without separate Live and Guide buttons on these models can cause Live to bring up the guide, the opposite of what you are experiencing and the fix is the same. This was designed into the TiVo software to make the newer dual tuner models compatible with older remotes.
DirecTV TiVo HR10-250
DirecTV STB Samsung SIR-TS360
DirecTV DVR HR20-100
TiVo Series 3 Comcast