Autodesk have released the 2nd Hot Fix (HF) for the 2011 flavours of 3ds Max and 3ds Max Design.

Please ensure you download the relevant version of the HF.

Autodesk 3ds Max 2011 - Download HF2 here
Autodesk 3ds Max Design 2011 - Download HF2 here

This HF covers many important areas including Viewports, Biped, CAT, and FBX from Revit issues.