I had a similar problem during my dxpedition. One record has been corrupted. If you are able to locate its number using partial import then OK, the problem is solved.
But if you have an ADIF backup, it might be easier to edit the ADIF file with a text editor (WordPad) since such a broken record is well visible when you scroll down the screen.
The broken record has another structure than the others. After deleting it, rename the file please (for safety), and then save - everything should work properly.
73 de Jacek SP5EAQ