Cannot insert/delete data of (custom) table

Hi all,

I created a new table to make the description of task-template can be defined based on language, and have setup the custom metadata.

Table definition is:

CREATE TABLE c_task_template_descr( 
 task_template_id NVARCHAR(32) NOT NULL ,  
 locale_code NVARCHAR(128) NOT NULL , 
ext_description NVARCHAR(256) , 
created_by NVARCHAR(32) , 
 created_dttm DATETIME , 
 modified_by NVARCHAR(32) , 
 modified_dttm DATETIME , 
 constraint c_task_template_descr_PK PRIMARY KEY CLUSTERED (task_template_id, locale_code))

Custom metadata - Relation Def:

Inserting the data from Task Template screen (custom) returned an error like shown in the screenshot below. 

FYI, the first data I inserted using SQL DML statement, insert.

Using XML message,  

<perform_mass_insert>
  <parameters>
    <select>
    </select>
    <update>
      <update_c_task_template_descr>
        <c_task_template_descr>
          <task_template_id>PM</task_template_id>
          <locale_code>DE-DE</locale_code>
          <ext_description>Testing Description DE-DE</ext_description>
        </c_task_template_descr>
      </update_c_task_template_descr>
    </update>
  </parameters>
  <transaction_size>100</transaction_size>
  <synchronous>Y</synchronous>
</perform_mass_insert>

I got this result:

<perform_mass_insert_result>
  <response>0 transactions executed successfull, 1 transactions caused error.</response>
</perform_mass_insert_result>

When the “Delete” button is clicked, nothing happens.

Did I miss anything in the table configuration?

Look forward to your input.

Thanks in advance,

~Juni