WebPart class [id] is referenced [1] times in the database

HI

Have got SP2010 installed - migrate from 2007 already completed but there are several warnings with WebPart like this:

[STSADM] [SPContentDatabaseSequence] [INFO] [5/18/2011 9:16:46 PM]: SPContentDatabase Name=sp_content
[STSADM] [SPContentDatabaseSequence] [WARNING] [5/18/2011 9:16:46 PM]: WebPart class [a21e5d41-9cab-1dd6-934f-fe972fd40238] is referenced [1] times in the database [sp_spsconten], but is not installed on the current farm. Please install any feature/solution which contains this web part.

AFAIK i should install smth web parts on the new SP server? But how can i find what web part i should install from its ID? (for expl [a21e5d41-9cab-1dd6-934f-fe972fd40238])