It would be helpful to know the exact error text.  You can also send screen captures to our support staff to further describe the problem.

I suspect that you may need to recompile the views.  You can do this from the Admin area, but the best way is to use the SplendidCRM Configuration Wizard. 

I would have expected the import to work fine.  By why didn't you use the normal upgrade process to go from 1.4 to 2.1?  For best results, you should upgrade by running the SplendidCRM Configuration Wizard on the old database.  It will do everything necessary to upgrade the database.

I suspect that the reason that you have multiple menu entries is because some of these records already existed in the 2.1 database before you imported the 1.4 data.  The import is rather blind and does not make any attempt to determine table uniqueness other than using the ID field.  In the case of menu items, this is not appropriate.

When you import an entire database, it is usually a good idea to truncate all existing data.