Chetan is asking you if the class is in a package named "customer", or if you've just placed in in a folder by that name. If it's the latter, I don't think there's any way to make it work. Either put the class into the "customer" package with a package statement, or put the checking applet at the top level of the jar file.
OK. You've been going back and forth between "customer" and "Customer" and "checking" and "Checking". Although Windows doesn't care about the capitalization of file and directory names, Java classes and packages are case-sensitive, and the "applet" tag has to match what you used in the Java source file, exactly. Does that help?