This is usually related to the order in which Access processes the form and its underlying data. If the textbox is evaluated before the query has returned a matching record, DLookup has nothing to work with and can produce an error. A good approach is to provide a fallback value instead of allowing the expression to fail. For example, Nz() can be used to return a blank value or zero when DLookup does not find a result. An IIf() condition can be used...

This is usually related to the order in which Access processes the form and its underlying data. If the textbox is evaluated before the query has returned a matching record, DLookup has nothing to work with and can produce an error. A good approach is to provide a fallback value instead of allowing the expression to fail. For example, Nz() can be used to return a blank value or zero when DLookup does not find a result. An IIf() condition can be used...