This issue is caused when you have a date assigned for DeadLine column.
1) Create a few folders on 76 database for a specific user on ToDo/WatchList with non-default value for eDeadLine column
2) Install 9.3 and configure Side by Side
3) Create same user in V9 database using Administration Web Site which has folders on 76 ToDo/WatchList (For example if you have user1 in 76 database which has folders on this user's ToDo/WatchList create the same user in V9 database)
4) Open Metastorm V9 Web Client and login with same username which was created in step 2 above
5) Click on either ToDo/WatchList
Actual Result: An error message "Specified cast is not valid" is displayed.
Expected Result: ToDo/WatchList should be displayed without any error message.
This issue has been fixed in hotfix 2 for MBPM 9.3.