Difficult. It sounds as though you are short of a necessary class in your jar file.
See if you can copy your jar to another directory, and unzip it (jars use virtually the same format as .zip files) and see whether all the classes you need are actually inside the jar.
Are there any external jar files which you had to import into Eclipse? I seem to have written about something similar yesterday,
here. Please see whether that is of any help to you.
CR