You tried to select a new symbol for a piece of irrigation equipment, but the irrigation symbols dialog box wouldn't open and you were unable to pick a symbol.
You clicked the symbol thumbnail in the Equipment Info dialog box, but the dialog box showing the symbols (pictured below) didn't pop up.
You're using a piece of equipment that uses our symbol families. As a result, you won't be able to just pick another symbol.
For example, you may have Family 2 selected for a bubbler.
2. When prompted to Pick symbol family, select the new family set you want to use for the equipment.
All placed symbols will be replaced by the symbol family you selected.