When programming, we use a language to speak to the computer. That language has syntax. If the rules of the syntax are broken, then the compiler complains and offers the term syntax error. In the same vein, all of the programming code that is written must be translated and compiled into something the computer can understand. If there are errors in that process, the compiler complains and throws a compiler error. These errors are given types, numbers, and brief English explanations. They offer the engineer a way to debug their programs in an orderly fashion.
Lastly as a program is running or during its runtime it may encounter problems during execution. When a problem arises that the software cannot resolve then it throws a runtime error, which means, while I was running I had a problem I could not resolve. The software, not the operating system gives the error. Through a self-monitoring mechanism called a trap, the software diagnoses itself, realizes it cannot go on, and traps to runtime error. There are many reasons why you will see a runtime error, the following are a few examples.
A runtime error can be caused by poor programming practices. If the engineer loads his software with memory leaks, it can cause a runtime error. If software patches are available, they can be installed to fix this problem. However, if no patches are available there is no way to fix this problem since it lies in the software.
If there is a program running on your computer that are poorly, it can affect other programs. In a Windows environment many things are shared, and if a rogue application steps into your arena there is a possibility for a runtime error to occur. In this case, you can shut down all other applications and then see if your software still has a runtime error.
Aging or damaged hardware
To a large degree software depends on the workability of peripherals in your computer. If you have an older computer, your hard drives are older than two years, you have recently had an electrical storm, of if your air cooling unit is out, degradation in service can occur. Any of these events can cause your software to throw a runtime error.
Virus or other malware
Viruses and other malware can run in the background undetected and can cause a lot of damage. They are not the leading cause of a runtime error, but can still lead to one. It's imperative that you scan your system with some type of antivirus software daily.
These are only a few of the causes for runtime errors but a rule of thumb is this. For new software that was recently installed, it could be the software itself. For software that was running before check your hardware and scan for viruses.