Hi Boris,

Your right, I found that the value actually is 0.000000000000455000.

IF your interested in the code which is giving me the error, here it is:

CALCULATE SUM (curGlEntry.nDebit) TO lnAmountDebit
CALCULATE SUM (curGLEntry.nCredit) TO lnAmountCredit
wait windows "lnAmountDebit = " + str(lnAmountDebit, 20, 18)
&& shows 2841.140000000000000
wait windows "lnAmountCredit = " + str(lnAmountCredit, 20, 18)
&& shows 2841.140000000000000


lnAmount = lnAmountDebit - lnAmountCredit
wait windows "lnAmount = " + str(lnAmount, 20, 18)
&& shows 0.000000000000455000

This.Value = IIF(lnAmount > 0.00,0.00,-lnAmount)

And obviously This.Value is not empty. I will replace with this
lnAmount = round(lnAmountDebit - lnAmountCredit,2)

Thanks again, at least there is a logical reason (not very smart from VFP) and I'm not crazy. ;-)