We use MicroStation CE Update 10. When attempting to export V8 DGN file to V7 DGN file by File - Export - Common File Types - V7 Format Design (*.dgn), the warning message "Error creating file ..." would come up. 
Despite the warning message, the V7 DGN would still be created. The problem is this V7 DGN is significantly smaller in file size with most of elements missing in there. Is there any settings I can do to get all elements exported? Or is this some kind of bug?
Thank you in advance for all your help.