Yuriko Tanii 

It might be helpful for you to share the proper error message by attaching the stack trace you get when you click on the small disk symbol in the error message.  But otherwise try opening the sdlxliff as if it was a new project and then immediately save the target.

Thank you Paul.

Let me attach the screenshot of the error. I hope this helps....

I appreciate any advice to solve this problem.

Yuriko Tanii 

Attaching the actual stack trace instead of a screenshot would have been more helpful!

However... try copying your sdlxliff for this project into another folder.  Then open this copy as a single file translation and immediately try to save the target.