I would like to reopen this case. Today I tried to make an export of all persons (ca 51000) and it gave me similar errors as mentioned above. In my case it was antivirus (MS security essentials). Although I was able to make the export if antivirus was turned off, I wouldn't say it is normal to turn off antivirus every time I make an export. I am 100% sure that it worked in v7 with same computer configuration.
br. Ular