Problem in Creating Jar file

Hello Friends
Today I m trying to use java after three years(after cllege).
The question is tht i m having one project which is in applets .I created class files
and one manifest file with this content only:

Main-Class:JRoffInit

I put this JRoffInit in this bcoz it contails Init() fn only.

now after tht when I try Command

Jar cvfm sample.jar manifest.txt *.class

then it shows some error tht r here below:
java.io.IOException:Invalid Header file
at java.util.jar.Attributes.read<Attributes.java:393>
-----------------.manifest.read<Manifest.java:182>
----------------.amnifest.<init><Manifest.java:52>
----------------.main.run<main.java:32>
----------------.main.main<main.java:1022>

Please suggest me some solution

Thanks & Regards
Yogesh