MKV2VOB application shouldn't be used anymore because its development has stopped. Because of that, the software might encounter errors when it comes to newer conversion methods and file support. Because of that, I recommend choosing another application that's constantly updated and available for downloading as well.
The Pazera Free MKV to AVI Converter might come in need. The software allows you to convert from MKV to AVI. Access the official website to download the application.
For MKV2VOB, right click the main executable and set the Properties > Compatibility to an older version except the one installed in your computer.