It depends on your OS (and OS version for Windoze)... Please, see the SL Wiki
(the user_settings directory is at the same level as the logs directory).
If it's a mesh, it might be a Bento issue. Try LL's official viewer (latest, Bento-enabled version): if you have the same issue with it, then report it as a bug in LL's viewer on their JIRA. If the object rezzes fine with LL's viewer and not with mine, then it's a bug in the latter: fill-up a proper bug-report, following the rules
to the letter, and especially giving a reproduction procedure (here, an object I could "see not rezzing" myself).