Does the chkMaintenance object is CheckBox?.. CheckBox have 3 value: 0 - Unchecked, 1 - Checked and 2 - Greyed.. You can not use boolean type field to set the check box field.. may be you have to convert it into 1 = True or 0 = False, so your code should be as follow:

chkMaintenance = iif(mrstCurrent("fldMenuMaintenance= True, 1, 0") depends on your needs..

Regards
Winan