Could you please give us some background information?
Are you exporting the photos as the unmodified originals or as edited versions?
Where is your Photos Library stored? In your Pictures folder or somewhere else?
Where are you exporting the photos to? To an external volume? And how many files are you trying to export at once?
Can you export the JPEGs one at a time, and to a folder on your Desktop? Or are some photos giving the same error, even when exported separately and to a local folder on your system volume?
Photos for Mac is currently having problems to export several photos at once, if two selected photos are having the same filename.Usually it is working better, when exporting in small groups, so there are no duplicate filenames within the selection. Or to export with a subfolder scheme, for example "Moment name".