failed Add new field in Resource Ledger Entry Table

Hi All,

I am facing difficulties in adding new column in my Resource ledger entry table.

I tried to go "Object Designer --> Table" ,click on "design" and add new field named "TaskA,TaskB,TaskC,TaskD", 4 new field and defined the datatype.
after that, i click on "Compile".... but just few minutes my navision will closed and when i log in again, i cant even access to my Resource Ledger Entry table. Shows not able to access the table's error. Luckily i try this at testing server.......
The table contains 984,299 line of data. 

Any Idea on why it happened and how to "backup" the table first, and restore it (include the data) when it corrupted while compile in progress?