报告公式导致运行时错误

Question

当我从Crystal Reports检查我的公式时，它找不到任何错误。但是当我运行我的项目时，我收到运行时错误。我该如何解决这个问题？

NumberVar t := 0;

IF 
(
    ToNumber({3ColTrailBalSumm.DR_BEFORE}) - (ToNumber({3ColTrailBalSumm.CR_BEFORE}) -
    ToNumber({3ColTrailBalSumm.CR_BETWEEN}) + ToNumber({3ColTrailBalSumm.DR_BETWEEN})) > 0
)
THEN
(
    WhilePrintingRecords;
    t := ToNumber({3ColTrailBalSumm.DR_BEFORE}) - ToNumber({3ColTrailBalSumm.CR_BEFORE}) - 
    ToNumber({3ColTrailBalSumm.CR_BETWEEN}) + ToNumber({3ColTrailBalSumm.DR_BETWEEN});
)
ELSE
(
    t := 0;
)