I can define a custom CRS in QGIS (v2.18.13, Windows 8) and conversion works fine and no error is reported when I hit OK.
proj4 is +proj=lcc +lat_1=49 +lat_2=77 +lat_0=0 +lon_0=-95 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs +ellps=WGS84 +towgs84=0,0,0
But when I go to use this CRS, there are no user-defined projections in the list.
A similar issue was raised here and here, but neither answer fixed my problem. May be a permissions issue, as the problem is not limited to the specific proj4 that I use, but I've enabled write access on all QGIS folder, still with no luck.
I'm experienced with GIS applications, but new to QGIS.