I just imported a bunch of multipatch features delivered in .mdb (personal geodatabase format) into City Engine.
1. Create a new file geodatabase.
2. Expand your .mdb in ArcCatalog and right click on a Feature Class and export 'To Geodatabase (single)' and select the file .gdb you created.
3. Use Nidhin's suggestion to get that data into CityEngine.
This workflow is kind of a pain since you must go feature class by feature class, but it might be scriptable. In my experience right clicking on the .mdb and exporting 'To Geodatabase (multiple)' didn't work.
Hope this helps!
thanks for your reply. i have solved the problem by switching the work space. the cause is that the same project is invovled in some other projects. althrough this makes my work more annoying, it works.