Regarding what you were saying about action engines, this is a common way I deal with error logging. In addition to adding logic to your program that decides what to do in case of an error (eg: ignore it and keep going, stop because it is critical, etc, basically this is what the document that ijustlovemath posted goes over), you also might want to log your errors so you can look at them later - that's where error logging comes in. What I often do is write an action engine that is in charge of my error logging, and it is basically just a VI that you call whenever you want to log errors that might be on the error wire (or you could even make it just log events in general, instead of only errors), so you wire in the error or a string about the event or whatever, maybe a priority level to be fancy, and then the VI takes the info and gets the date and time and formats that and appends it to a file that it is keeping on an uninitialized shift register (you will want to write the VI so it checks if it is the first time it is called and if so, creates a file and puts that on the shift register). Hopefully this makes sense. If not, I can explain more.
--Hope
