Today i run into error
Invalid signature file digest for Manifest main attributeswhile running my java web start applet.
I wondered for a while and finally found the reason - yesterday I modified my .pfx key for signing applet, but manifests in jars merge with each other - so I really had jar with invalid digest.
To fix it, I just had to remove META-INF folder from all my jars, add them manifest again and re-sign them. You can remove it with any archiver - for example, with 7-zip.