An error may occur if the Glass Database is used to map glazing properties in the model which has just been modified or deleted. This may occur if the Add Windows or Add Curtain Walls feature is used and then this is reversed (the glazing that was created is then removed/undone). Attempting to apply properties to this glazing in the Glass Database to Surfaces which no longer exist in the model may cause an error.
This may also occur if properties have been applied to glazing which is subsequently deleted. This is not an error but simply a referencing issue where model elements are created or removed, and dependent properties need to update. Users are advised to work methodically and allow the application to refresh and update as changes are made. If major changes to the model geometry are to be done, it is best to close the application, modify the model and open the application when you are ready to analyze again.