Failed to save target. Object reference not set to an instance of an object. mqxliff file.

I have to translate a mqxfill file in Trados 2015. When I try to save the file in mqxliff format I get the message "Failed to save target. Object reference not set to an instance of an object". I read online that it's a problem with tags. I run verify check and everything is in order. Is there any way of fixing this? The client want mqxliff files back.