[RESOLVED] The SkinID value is not defined the theme or stylesheet theme

I'm working on Themes, I've created a theme name "Blue" in that a Label with "SkinID:textLabel". When I'm referring the label in the web page the error has occured : "The SkinID value is not defined the theme or stylesheet theme". However I've created an ImageButton as well and it is working perfectly, what would be the error?

Thanks in advance,

Sri Hari