I have a mosaic of GeoTiff files and a colormap to style it.
Most of the time, the Layer Preview page fails to display an image, giving the error "Failed to encode the PNG".
With the standard "raster" style there are no errors.
Loading the same file with the single GeoTIff store produces no errors.
A sample image, sld and error log are attached.
Place the attached sample.tif file in an empty folder
Create an ImageMosaic out of that folder
Create a new style with the attached test.sld definition
Assign the style to the mosaic
Preview the layer
The "tiled" mode in the preview doesn't seem to be affected in this example
Windows and Linux
Platform independent binary package