We recommend that you install the latest OpenSim compatible Firestorm viewer. Firestorm is a free, open source viewer that is community supported.
It is a trusted viewer that is used by hundreds of thousands users on both OpenSim and Secondlife.
Quick download links:
Firestorm Viewer for Windows
Firestorm Viewer 6.6.17 this is the most stable, reccomended viewer
Firestorm Viewer 7.1.11 this is the latest version with the latest freatures, and may experience some problems.
Firestorm Viewer for Mac
Firestorm Viewer 6.6.17
this is the most stable, reccomended viewer