#error when summing numbers in report builder?

Question

I am trying to summarize some numbers in a group, and sometimes #error will be displayed instead of the actual number. I understand that this can happen when dividing by 0 or when there are zeros in the data set, but in the data set I see only real numbers. The numbers are not large enough to cause an overflow, and I am sure that the expression is correct, because #error displayed only for a certain combination of parameters.

Is there another reason why I see a #error message?

To be clear, the formula =Sum(Fields!Number.Value)

Edit: Any of the aggregation functions also leads to this message.

Answer 1

Sometimes SSRS decides that the number field returned from the dataset is text. Then many vb functions will fail.

See if the number converts to decimal value:

 =SUM(CDEC(Fields!Number.Value))