qgis - Why do I get "Failed to transform" when reprojecting from WGS84 to Google Mercator?

I am attempting to re-project a vector shapefile from Natural Earth, following a qgis tutorial. Another user reported this error, but a solution has not yet been reported.

Given this post, and the last line of the error, I suspect that there is something wrong with the CRS setting, etc. Though, I have not been able to identify it.

   Export to vector file failed.
Error: Failed to transform a point while drawing a feature of type 'ne_10m_admin_0_map_units'. Writing stopped. (Exception: forward transform of
(3.141593, -1.570796)

PROJ.4: +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +to +proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs
Error: tolerance condition error)

I am using qgis 1.8.0 on Ubuntu 12.05. Thanks for the help!

Answer

If you look at the extent of the layer, you get:

xMin,yMin -180;-90 : xMax,yMax 180;83.6341

Google Mercator projection is only valid between +/- 85.0511 degrees North/South, but the dataset contains also the south pole.

EDIT: The value of yMin=-90 forces the error in projecting to Google Mercator. The tutorial has a dataset that ends at -89.9998, which is nearly the same, but does not compute to inifity.

So you have to delete the objects around the south pole, to save the layer in Google Mercator projection.