I install QGIS 2.6 but QGIS-OSGeo4w didn't install GRASS functions. I removed other versions from control panel (feature and program) but, in all of times that I install it, I confront with this error when I open it:
QGIS couldn't find your GRASS installation. Would you like to specify path (GISBASE) to your GRASS installation?
I choose all of folders but all of efforts was unsuccessful.