Avira error 503 occurs due to the incomplete installation of the software. If your operating system refuses to support the Avira Antivirus software, the error code 503 will appear on the screen. Otherwise, you can identify it when you receive a pop-up of USB drive error, frequent popping up of permission errors, or other pop-up errors. This error will crash your Windows program, damage the OS, restrict the running the extension files, and create issues in the Windows registry. If you wish to resolve the Avira Antivirus error 503, follow the below-mentioned methods.