<p>Yesterday I was having a heated debate with a coworker on what would be the preferred error reporting method. Mainly we were discussing the usage of exceptions or error codes for reporting errors between application layers or modules.</p>

<p><strong>What rules do you use to decide if you throw exceptions or return error codes for error reporting?</strong></p>

I normally prefer exceptions, because they have more contextual information and can convey (when properly used) the error to the programmer in a clearer fashion.
On the other hand, error codes are more lightweight than exceptions but are harder to maintain. Error checking can inadvertently be omitted. Error codes are harder to maintain because you have to keep a catalog with all error codes and then switch on the result to see what error was thrown. Error ranges can be of help here, because if the only thing we are interested in is if we are in the presence of an error or not, it is simpler to check (e.g., an HRESULT error code greater or equal to 0 is success and less than zero is failure). They can inadvertently be omitted because there is no programmatic forcing that the developer will check for error codes. On the other hand, you cannot ignore exceptions.
To summarize I prefer exceptions over error codes in almost all situations.