There is no known in-combat error message recorded so far.
Can you be more specific?
What weapon?
Use on what?
What does the error message say?
What OS are you using?
Are you using any mods?
Have you used command line cheats?
Are you running the game on an emulator?
What Game version are you running?
...
Maybe my explanation wasn't so good. The game itself has a normal English character set.
I was thinking that your operating system might use a special dual Unicode character set such as Japanese, Chinese, or other languages with many characters use and that that might be the cause of the error you observed.