>I tried to set to true using the properties window, but after selecting the true from the drop down list it set to false automatically. Can you help me on this....

From the DOcs:

"For combo box controls, the ReadOnly property cannot be set to true (.T.) when the Style property is set to 2 – Drop-down List."

Use enabled or Return .F. in the WHen event. THe thing is, if a Drop DOwn list is readonly, there is absolutley no point to even access it.