Unfortunately, your question is a bit short on details. Can you be more specific? For example, can you take a screenshot of the exact message you are getting?
To where are you trying to export the file? It's probably a silly question, but are you absolutely certain there is enough space on the hard-drive to which you are attempting to save the file?
Again, you might get more replies if you can be a bit more specific in your problem statement. The more (clear) detail, the better.