The DIXF wizard is sometimes buggy, try to follow the custom/manual creation of the entity, which is also documented on MSDN.
As a comment for the Product attributes, please note that it is using the SC-sc structure, so those are tables with inheritance. The individual values in the attribute are stored in different tables, one for each element type, like string/real/int64 etc.
First I would recommend to get a solid understanding of how the values are stored in the Product attributes tables, then you may try to implement the custom entity.
Others have attempted this as well, see the topic below:
community.dynamics.com/.../123571
One of our fellow community member was kind enough to share his solution on this, available on the link towards the end of the topic.