Sorry, I haven't seen that error on our system. What release of Desktop Central are you running? 90023 is the latest publicly available, I think, but if you contact Support you can get a newer hotfix than that. I'd guess that error is fixed in a hotfix.
Couple of suggestions:
It sounds like it might be related to either your Java Runtime version or something in your Java (or browser) cache. Have you tried clearing your browser cache as well as your Java cache, then going back into Desktop Central and re-trying the create package process?
Also, on the Software Deployment tab, in the lower left margin, have you tried the "Sync Application Details" <Sync Now> button? If your templates are up-to-date, you should see the Adobe Flash Player 14.x in the list. If you don't see the newest versions of the templates, the package creation probably won't work.