Dinkey Pro/FD dongles can only be accessed by one thread or process at a time. This error number indicates a problem enforcing this constraint.

On Windows 8 and newer, this error occurs most often in Universal Windows Platform Apps (previously called Windows Store apps or Metro-style apps) locked to a Plus or Lite dongle. Windows Store apps are currently not supported by Lite or Plus dongles. You must use Dinkey Pro Net or Dinkey FD Net dongles to protect Windows Store apps.

If you receive the error 504/13 on Linux then you need to upgrade to Dinkey Pro/FD SDK 7.5 or higher and protect your software again using this version. This problem is caused on some systems that implement a new Linux security update.