OeyEnc is not compatible with Windows 8.1. According to the system requirements, the application works with the following versions of Windows:
- Windows 2000
- Windows XP (x86 & x64 Editions)
- Windows Server 2003 (x86 & x64 Editions)
- Windows Vista (x86 & x64 Editions)
You can find more information about this on the official website of the product.