Module Pool While calling Tcode

Hi frnds,

I have 1 requriment for that I have to write Module Pool.

I have created two button.

FCT Code- MM01

FCT Code- MM03

I want when FCT code MM01 calls ( It will call Tcode - MM01) & for MM03 calls the Tcode MM03,

Where I will write code in PBO or PAI.

I have writtern my code PAI.

MODULE USER_COMMAND_1000 INPUT.

CASE SY-UCOMM .

WHEN 'ME20'.

CALL TRANSACTION 'ME20'.

ENDCASE.

ENDMODULE. " USER_COMMAND_1000 INPUT

But here While calling Tcode- ME20 it give me dump

Plese help me to resolve thise issue.

Regards.