Java SE (Java Platform, Standard Edition)

I signed a jar (which is a standalone application) with:
C:\>jarsigner -keystore myKeystore myJar.jar

I verified it with
C:\>jarsigner -verbose -verify myJar.jar
It was OK.

I updloaded it to my web site via ftp.

When I try to to downlod it via Java Web Start, I get a java.util.zip.ZipException.

If I try to verify it again with jarsigner, I get:
jarsigner: java.util.zip.ZipException: invalid END header (bad central directory offset).

Can anyone tell me where the jar file may have been corrupted ?

Thanks a lot

Norberto