Hi Conner,
I’ve tested this myself and it works fine for me. Allow me to ask a few questions for clarification.
Are you customizing a stock report or building your own from scratch?
Are you running any custom scripts on the report?
What data type is the field you are trying to apply this to?
I’m unable to replicate this error. It seems that even if I apply the format string to an incorrect data type, Report Designer is intelligent enough to remove it or simply ignore it.
You can try having report designer build the format string for you. If you select the ellipsis ‘…’ button, the FormatString Editor will be displayed. Select Currency > Custom and enter “€0.00”. This simply builds the format string the I provided you previously.
-Audisho