Need help: cannot save as .mdl due to special characters

I want to save a model into .mdl format. But there is an issue as follows:

Does anyone know how to quickly find the specail charaters and remove them?

Thanks

[Jan]

Is there really this red ellipsis in the message? If not, it might be trivial to find the special characters just be seeing the file name. I cannot guess, what the file name is or how you have defined it, but the problem should be trivial - actually.