String Required Web Error

I have two ClearQuest checkboxes. Both must be 1 (yes) to be counted in a Crystal Reports formula. My formula:

If {ClearQuest.THREA___EP_LIST_CKBOX_ACCURATE} = 1 and {ClearQuest.THREA___P_LIST_CKBOX_COMPLETED} = 1 then 1
else 0

Then I use a Crystal Reports Running Total to sum the formula across a number of records.

Works fine in the ClearQuest client; however, when I run it on the web I get an error:

Exception in formula '{@Total-Accurate and Complete}' at '1': A string is required here.

What must I do to clear this error. I've tried it using both string and integer checkboxes - same error.

Thanks in advance.