When writing a reporting services report sometimes it is impossible to evaluate all errors in desing mode.   Occasionally, you may run across that the report runs but a single cell my return a #ERROR instead of the value expected.   Sometimes this is caused by an invalid type being sent through a format expression for example.   To eliminate the #ERROR, first check the data source to ensure the values are what you expect, then secondly code your expressions to satisfy your output using conversion formulas such as CINT().