Jar command line returns IO error

Jar command line returns IO error

When I type jar cvfm file_name.jar manifest.txt *.class in command prompt
I get this error:
java.io.IOException: invalid header field
at java.util.jar.Attributes.read(Attributes.java:410)
at java.util.jar.Manifest.read(Manifest.java:199)
at java.util.jar.Manifest.<init>(Manifest.java:69)
at sun.tools.jar.Main.run(Main.java:172)
at sun.tools.jar.Main.main(Main.java:1177)
I've never gotten this error before and I can't find anything on it, what
does it mean?