we created a copy of existing database exceptions measure to collect metric by agent. this effects the default "Errors" dashlet, by showing the exceptions count double.
For the newly created measure for database exceptions are you able to see the details tab in the measure configuration window? There should be an option to create a measure for each agent which would give you what you want. You could also just create an errors dashlet then filter the dashlet by the corresponding agent/host to get that type of filtering. hope this helps.
Have you tried checking the box on the original measure to create a measure for each agent as well as one for each application? The Errors dashlet by default shows the total and thus shouldn't be affected by this change but you will then be able to chart the counts by agent if that is what you are aiming to do.