A lot of people have been complaining that dances and animations that they've bought from reputable SL merchants like Henmations, Akeyo, and Vista have been removed from their inventories.
When someone submits a DMCA notice to Linden Lab, alleging that another person has infringed their intellectual property rights, LL removes the allegedly infringing content from Second Life...including from the inventories of everyone who owns it.
However, sometimes the DMCA notice is wrongfully made. Also, sometimes, the LL intellectual property police make a mistake and remove things that are NOT a subject of the DMCA action but that only have a similar name. It appears that this may have been the case in this instance.
Once the mistake is straightened out, the missing items should be returned. However, if you are not content to wait and see if this happens, go to the store where you bought your deleted content and make use of their re-delivery terminal, if they have one.
For current discussion of the issue, see this forum thread: http://community.secondlife.com/t5/General-Discussion-Forum/Firestorm-AO-in-viewer-animations-abscounded/td-p/2874423