Version in the thumbail

What is the meaning of the parameter version in the thumbnail API:

by example, it’s works:

http://cfvod.kaltura.com/p/2288691/sp/228869100/thumbnail/entry_id/0_g9ikhwwa/version/100002

but not it:

http://cfvod.kaltura.com/p/2288691/sp/228869100/thumbnail/entry_id/0_g9ikhwwa/version/100001

Could some one to give us an example?

thanks

lluís