Error when trying to open file for translation in Trados Studio: "Unknown exception when generating layout for segment x"

You are trying to open a file for translation in Trados Studio but when the Editor window initializes you receive this error message:

• Unknown exception when generating layout for segment x (internal row y).
• Click Cancel to suppress background error messages for this control.

After this some of the characters are missing or displayed wrong in the source segments.

In a German Studio User Interface the error message will be Unbekannter Ausnahmefehler...

Check that the font list of your operating system is complete and try to install missing/ corrupted fonts. See this external article for reference.

As a workaround, try these steps:

1. Go to File -> Options -> Editor -> Formatting display style -> Show all tags but do not show formatting 
2. Close Trados Studio
3. Reopen the file

Note: this is just a display issue, the files is not corrupted.

This article provides a more technical workaround that includes modifying the registry:

Error message when using certain characters in source or target language: Background Layout Error

This is more common for languages that require special fonts such as Japanese, Korean, Romanian, Russian, etc...
Sometimes fonts may be missing or get corrupt on the Operating System where Studio is ran. Because of this Studio does not know how to handle some of the characters.