MiteBonu,
There is jarsigner -verify and some -verbose mode that may shed more light.
Are you trying to apply the cert to a newly compiled unsigned jar file?
Most of these cryptic errors are password/alias related.
Couple of other tips, when you get the p12 or pks, you need to make sure the entire chain is included and not just your keys. A lot of keys just have yours, and you need to add back in the root CAs before using.
Also you need to find the "Alias Name" used the cert in order to correctly apply it.
Regards,
Stephen