Lock Data: Enqueue and Dequeue

Im trying to lock data from vb.net but it didnt work out.

I pass the variable to my function module and inside the function contains below codes.

eg:

CALL FUNCTION 'ENQUEUE_EZCOL06'

EXPORTING

MODE_ZCOL06 = 'E'

MANDT = SY-MANDT

ZBUKRS = code1

ZGJAHR = code2

ZRPTNO = code3

_SCOPE = '2'

_WAIT = 'X'

EXCEPTIONS

FOREIGN_LOCK = 1

SYSTEM_FAILURE = 2

OTHERS = 3.

I open multiple screen (VB.net) but still it didnt lock the data. I dont know where it gone wrong. But when I try in SAP itself it works. I open multiple session and it detects and it locks the data.

Please help.

Thank you.