Here are our suggestions on resolving the problem:
1) Do you experience this problem in Internet Explorer only? If it exists only in IE, it is most likely due to that you are loading more than 31 css files. You can find information about this problem in this blog post: Internet Explorer CSS limits
The solution for this browser limitation is to manually combine the different Telerik control skin files in one or several CSS files
in which you link the removed CSS files
one by one using @import declarations
2) The second reason for the problem is that the URL that should point to the /Common/CommandSpritesLight.png toolbar sprite image of RadEditor is wrong. You can check the path in FireBug and correct it until the image is loaded. You can find more information about RadEditor custom skins in this article: Creating Custom Skin for RadEditor
You should also check whether the Common skin folder contains the CommandSpritesLight.png, /Common/CommandSpritesDark.png, CommandSpritesLight.gif and CommandSpritesDark.gif files.
3) If you unable to solve the problem, please provide a live URL to the problematic page, so that we can examine it on our end with Firebug and IE developer toolbar and provide a solution.
Another approach is to open a support ticket and send a sample working project along with your custom skin that demonstrates the problem.
the Telerik team
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