ok. make sure you don't have any hanging geopak.exe processes in your task manager in windows. then,
Delete everything under the 8.11 folder
On Vista the location is
C:\Users\yourusername\AppData\Local\Bentley\MicroStation\8.11\
On win 7
C:\Users\ yourusername \AppData\Local\Bentley\MicroStation\8.11
on WinXP
C:\Documents and Settings\ yourusername \Local Settings\Application Data\Bentley\MicroStation\8.11\