Hi Pawel,
just append this line to your code:
oMyEdit.Item.SetAutoManagedAttribute(SAPbouiCOM.BoAutoManagedAttr.ama_Editable, 15, SAPbouiCOM.BoModeVisualBehavior.mvb_False);
The problem you are experiencing results from the auto from mode managment of SBO ( different mode -> standard value : editable )
regards,
Maik