QGIS raster clip error: Cutline not of polygon type

Is your polygon and raster in the same projection? If not, try projecting to a common projection, as mentioned here:

Raster file clipping error.

Please see this post.

Receiving GDAL Clipper Error from QGIS?

1) One of the layers is missing projection information. Post both your layers so we can take a look.

2) A polygon that has some issues such as self intersecting (unlikely). It is almost always one. You need to project or project both layers into a common format.