Hi,
A parent id for all of your products ?
When you specify a parent id, it means that you are importing a product variant. A variant can't have a category because it's not a "main product" and the categories are stored in this one.
So, depending your CSV, yes, it could be a problem for the import system.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.