Error in field in textbox in detail section

[jonomac]

Is it possible to pull back one field in the detail section on a report under certain circumstances and another field at all other times as per the below code?

textbox name = am_units_calc

=IIf([id_activity_type]="Trading Fees",[am_units_calc],[am_per_unit])

The textbox is currently producing an error whether or not Trading Fees is returned on that particular line.

Thanks

 

[jonomac]

I solved it, i needed to rename the textbox to something else other than the fields i was trying to populate it with....

eg this works fine...
textbox name = txtAmount

=IIf([id_activity_type]="Trading Fees",[am_units_calc],[am_per_unit])