Please go to the Preferences of the Lightroom and under the general tab un-check "Show add Photo screen"
Restart the lightroom and try again
Thanks but this did not help me.. The export function is one of many problems I found on the latest version of LR (drag and drop to folders, map function, slide show, export, delays when entering the Develop mode.....). It seems like it take forever to load something in the system because sometimes these functions do work.
Many, many people have reverted to the last stable release, CC 2015.1.1 / 6.1.1: How do I roll back to Lightroom 2015.1.1 or Lightroom 6.1.1? Wait until Adobe cleans up the mess and releases 2015.3 / 6.3, and let others do the beta testing.