What does Windows error code 15104 (ERROR_MUI_INVALID_ULTIMATEFALLBACK_NAME) mean?

ERROR_MUI_INVALID_ULTIMATEFALLBACK_NAME

ERROR_MUI_INVALID_ULTIMATEFALLBACK_NAME indicates that the resource configuration has an invalid fallback language name. The fallback is used when no resource file matches the requested UI language.

What to check for ERROR_MUI_INVALID_ULTIMATEFALLBACK_NAME

• Verify the fallback locale written into the MUI resource configuration.
• Ensure that the corresponding fallback resource file is actually included in the installation.
• Keep the fallback definition synchronized with the language-neutral binary and all localized resource files.

Microsoft: MUI Resource Management

Microsoft: Deploying multilingual resources

Microsoft: About Multilingual User Interface

Where the result is returned

This result is Win32 system error 15104 (0x00003B00) from winerror.h. AllStat describes it as “The RC Manifest has invalid ultimatefallback name.”