NaN error appears when it should not

My XLF program is showing a NaN error when it should not. There is an input text pointing to a particular cell and another text label points to that same cell, and is showing the NaN when I preview the SWF. The FAQ on the Xcelsius support site states that when a NaN error is showing that it is expecting a numeric value when there is none. This confuses me because the cell in question is supposed to display text, not a number, based on the results from other cells. Similarly, my input text is not configured to be a numeric format.

Here is the actual formula in the cell which appears to be triggering the NaN error in Xcelsius:

<code>

=IF(OR(ENGINE!B4=0,ENGINE!B7=0,ENGINE!B8=0,ENGINE!B9=0,ENGINE!B10=0), "Please fill in the required fields", ENGINE!B31&" "&ENGINE!B32)

</code>

Thanks in advance.