While trying out the different themes on my local web server I came across a problem with the site icon, the WordPress replacement for the favicon.
After making the image to the recommended size and naming it siteicon.png I clicked on “Select site icon”, uploaded the file and then selected it. A new screen came up asking me to “Crop image” and it was when clicking this that the error “WordPress will not crop “ came up.
After a quick search of the Internet I discovered that WordPress uses the GD Graphics Library for dynamically manipulating image. As this library is already included in PHP the simple solution was to uncomment the line “extension=php_gd2.dll” in php.ini.