The “Object reference not set to an instance of an object” error message may sometimes occur when you attempt to log in, or while you are accessing a snap in.
To resolve the issue:
In the Run box, type one of the following command.
For Windows Vista or Windows 7:
c:\Users\UserProfile\AppData\Local\Juris\
For Windows XP:
%USERPROFILE%\Local Settings\Application Data\Juris
Test to ensure that the renaming resolved the issue.
Note
If the workstation is using cache enabled mode, the cache file might also need to be rebuilt. Note that this can also be caused by not having .net 3.5 installed, which is required for Jruis 2.4 and above.