CheckBoxField returning string?

[absentia.no]

I am using a datagrid and have a column which should consist of
checkboxes. The datafield that generates the checkbox-column is bit,
but I am getting this format error:
System.FormatException: String was not recognized as a valid Boolean.

If I use boundField instead everything works fine, but I want to use
the checkboxes as it seems very odd to make my users type in 0 or 1
manually to decide wether to turn off or on.

Also, I have made a custom update method which uses bool as the input
for the checkbox-variable.

What am I doing wrong?
royend.