Hello Sine,
I tested this LSMW with all the structure required and it works well in IDES , Follow these steps and try
1.You have to change customization per note 1120544 - LSMW for task list
goto transaction SM31
2. Please find attached example in IDES, you may need to adjust the source fields per your requirements import the project attached by using the menu option extras->import project
of this file
3. place this source files in the C:\temp ( or change it as required )
Source files:
.
Good luck
Regards,
Ziv