Changing Textboxes On A Multipage Control

Last weeks I've had too few spare moments to answer questions, hope to pick that up soon. I have a strange problem now with some checkboxes on a multipage control.

Please see the attachment.

I want to check all the 5 boxes on a page if the box above is checked, and vice versa, uncheck them all if the box above is unchecked. I use code of Dave Hawley to loop through the checkboxes.

This doesn't work, but oddly enough, it works if I insert a MsgBox in the code.