What version number is your Lightroom? What operating system? Is it 32bits or 64bits?
How much memory does your computer have? How much space is free on the hard disk you are exporting to? How many photos are you exporting at one time?
Can you show us a screen capture of the settings in your export dialog box when you are experiencing this problem? It may require several screen captures because the export dialog box is very tall.
We are running Lightroom CC (and just updated so what ever the latest version is)
Here is a screen shot of the computer details. 32 bits of memory. The lightroom catalog is on an external HD and is accessed though an array system "Thunderbay 4"
Lightroom is currently frozen on me, but the export dialogue box is exporting to a hard drive and the only setting is under file handling which is set to Original. Let me see if I can un-freeze it and get a screen capture.
oops sorry, exporting over 5000 photos. Something we do all the time. In the past (with the old cameras, smaller files) It was never an issue. Ya lightrom would be a little slower. but you could still do thing.
What happens if you export in smaller batches of photos, say 200 at a time?
When exporting 5000 files all at once, those smaller files will make a big difference.