Do you export with negatives or/and previews?
Just made a test import and export of a 23K catalog - no crashes on Win7 with 4.1RC.
Crashes on multiples of 500 suggest that it might happen at database commits. Try optmizing your target catalog.
thanks, Cataog exports were Smart Collections of a days worth of images. From the Smart Collection, I selected export as a Catalog so all things associated with it would go.I do not opt out of anything. After a LR4.1 uninstall/install we were able to get pass the 500 series issues but after importing all the images, the programs crashes every time...images to move and they look okay...we have taken out IE9, optimized all catalogs, tried totally new catalogs, large catalogs, small catalogs, all with the same result of a crash now just after the last image moves.