FileNotFoundException is a prevalent error in C# that arises when a program attempts to access a non-existent or deleted file, caused by issues such as incorrect file names, altered file locations, or wrong paths. This exception, part of the IOException class, is typically handled using a try-catch block, where developers can manage the error by either displaying a message or creating a missing file with File.Create(). Using File.Exists() before file access can prevent this exception by checking the file's existence, returning true if it exists. Examples demonstrate different scenarios of FileNotFoundException, including direct file reading attempts and assembly load failures, with stack traces aiding in debugging. Tools like Rollbar can enhance error management by providing real-time tracking and analysis, thus streamlining the debugging process and easing the deployment of reliable production code.