From errors you might have 2 issues:
- Probably you have some characters not fitting into code page
- Field is too short and you have too long data
Probably 2nd error is causing the other. Unfortunally weak error reporting is one of side effects using SSIS.
And little advise, don't use NTEXT rather NVARCHAR instead. It easier to work with NVARCHAR: nvarchar(max) vs NText