>We have a table which contains the file name of some recordings. Whenever we change record, we have to verify if we have a file name in the field. If we have a file name, we assign the file name to the MMC property and issue an Open command so we are ready to play the file. If not file name is present, we just call the Close command which will disable all buttons on the MMC toolbar.
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>However, whenever we do that, this makes the MMC toolbar to display disable and enable. So, we would like to avoid the visual display of that. So, we tried to set LockScreen to .T. before doing that and it doesn't change anything. So, it seems LockScreen doesn't take effect on MMC. Is there an option in MMC to do the same?

Vlad's told you the reason (the control is it's own window and LockScreen, therefore, has no effect). What you have to do is get the window handle of the form (I'd suggest using the Foxtools functions _WFindTitl() and WhTohWnd()) and then use FindWindowEx() or GetWindow() to locate the control.

It would help if you know the class name of the control. You can retrieve that using Spy++ or if you don't have that, my SpyFoxFox from the downloads to find it.

There's an example of using FindWindowEx() (which I think would be preferable) in the April VFUG newsletter on dealing with the Calendar control. If you need any assistance, just post back.